diff --git a/README.md b/README.md
index b925f13..373c6cd 100644
--- a/README.md
+++ b/README.md
@@ -4,17 +4,13 @@ This repository overlays the [upstream nixpkgs-channels
 repository](https://github.com/NixOS/nixpkgs-channels) with fixes and
 additional packages to create a repository suitable for use on Compute
 Canada HPC clusters.  It is available to use by default on Compute
-Canada clusters.  It's layout is modelled after the [upstream
-nixpkgs](https://github.com/NixOS/nixpkgs).
+Canada clusters.  It's layout is modelled after the upstream one.
 
 
 # Using
 
-This repository overlayed onto the latest [upstream
-nixpkgs-channel](https://github.com/NixOS/nixpkgs-channels) is the
-default channel on Compute Canada clusters.  To update to the latest
-version (i.e., the last one for which all overlays built successfully)
-do
+To update to the latest version (i.e., the last one for which all
+overlays built successfully) do
 
 ```bash
 nix-channel --update
@@ -39,8 +35,8 @@ To install (or update) a package, specify the packages attribute to
 nix-env --install --attr attribute
 ```
 
-where `attribute` is a placeholder for the attribute that designates
-the desired package (e.g., `emacs`).
+where `attribute` is replaced with the attribute that designates the
+package (e.g., `emacs`).
 
 ## Removing
 
@@ -88,7 +84,7 @@ again.
 
 # Developing
 
-To add to this this repository, `git clone` it into a local directory.
+To add to this repository, `git clone` it into a local directory.
 
 ```bash
 git clone https://git.computecanada.ca/nix/ccpkgs.git
@@ -106,41 +102,42 @@ git clone https://github.com/NixOS/nixpkgs-channels.git -b nixos-$(< .version) u
 
 ## Layout
 
-Longer term overlays, like package additions, are put in the *pkgs*
-subdirectory.  Shorter term overlays, like temporary upstream
+Longer term items, like package additions, are put in the *pkgs*
+subdirectory.  Shorter term items, like temporary upstream
 workarounds, are placed in the *temporary* subdirectory.  The
 *pkgs/all-packages.nix* and *temporary/all-temporary.nix* files are
 applied as [overlays](https://nixos.org/nixpkgs/manual/#chap-overlays)
 on top of the the upstream nixpkgs-channel.  This means attributes
 defined in them (first *all-temporary.nix* and then
-*all-packages.nix*) will replace attributes defined in
+*all-packages.nix*) will replace or augment attributes defined in
 nixpkgs-channel.
 
 Inside both of these files, the default scope is the final attribute
 set (i.e., after all overlays have been applied).  The final, prior
 (before the file's overlays are applied), and next (after the file's
 overlays are applied) attribute sets are also available under the
-top-level attributes `pkgs`, `super`, and `self`.  Consider the
-`emacs` attribute for example.  `emacs` and `pkgs.emacs` refer to the
-final `emacs` definition.  The prior (before this overlay) and next
-(after this overlay) definition are also available though
-as`super.emacs` and `self.emacs`, respectively.
+attributes `pkgs`, `super`, and `self`.  Consider the `emacs`
+attribute for example.  `emacs` and `pkgs.emacs` refer to the final
+`emacs` definition.  The prior (before this overlay) definition is
+available as `super.emacs`, and the next (after this overlay)
+definition is available as `self.emacs`.
 
 ## Adding
 
 Packages are added by creating an appropriate *pkgs/.../package.nix*
-or, if more multiple files are required,
+or, if additional patch files and such are required,
 *pkgs/.../package/default.nix* expression, where `package` is a
-placeholder for a suitably descriptive (e.g., `emacs`), add then
-adding a `package = callPackage ...` line into
-*pkgs/all-packages.nix*.  This makes available under the attribute
-`package`.
+placeholder for an appropriate name (e.g., `emacs`).  This expression
+is then assigned to an attribute by adding an `attribute = callPackage
+...` line to *pkgs/all-packages.nix*, where `attribute` is replaced
+with the attribute that will designate the package (e.g., `emacs`).
 
 The easiest way to create the nix expression, is to look through the
 existing overlay expressions, find one that is suitably close to what
 is desired, and then duplicate and modify it.  [Upstream
-nixpkgs](https://github.com/NixOS/nixpkgs) expressions can also be
-used as a starting point as they also follow the exact same format.
+nixpkgs](https://github.com/NixOS/nixpkgs/tree/master/pkgs)
+expressions can also be used as a starting point as they also follow
+the exact same format.
 
 More information on creating packages can be found in the [Nixpkgs
 Contributor Guide](https://nixos.org/nixpkgs/manual/).  More
@@ -157,10 +154,9 @@ Nix expressions can be build from the top-level directory by using the
 nix-build --attr attribute
 ```
 
-where `attribute` is replaced with the appropriate attribute (e.g.,
-`emacs`).  It is highly recommended to do this before pushing any
-changes to the master repository as any breakage will prevent further
-releases of the channel to the clusters until fixed.
+It is highly recommended to do this before pushing any changes to the
+master repository as any breakage will prevent further releases of the
+channel to the clusters until fixed.
 
 ## Debugging
 
@@ -168,9 +164,9 @@ The `nix-shell` command can be used to enter a non-sandboxed version
 of the build environment from the top-level directory.  Passing the
 `--pure` option causes it to purge the environment.  RHEL and Fedora
 do not guard against multiple evaluations of the */etc/profile.d*
-scripts though, so the environment will re-initialize itself from
-*~/.bashrc* script unless it is modified to not source */etc/bashrc*
-when `__ETC_PROFILE_SOURCED` is set
+scripts though, so the default *~/.bashrc* will restore it unless it
+is modified to not source */etc/bashrc* when `__ETC_PROFILE_SOURCED`
+is set
 
 ```bash
 sed -i -e 's|^\(\s*\)\(\. /etc/bashrc\)\s*$|\1test -n "$__ETC_PROFILE_SOURCED" \|\| \2|' ~/.bashrc
@@ -192,13 +188,13 @@ somewhere writable (e.g., */tmp*)
 ```bash
 export NIX_ENFORCE_PURITY=1
 NIX_BUILD_TOP=/tmp/nix-$USER
-
-mkdir "$NIX_BUILD_TOP"
-cd "$NIX_BUILD_TOP"
-mkdir out
-out=$PWD/out
+out=$NIX_BUILD_TOP/out
 prefix=$out
 ```
+```bash
+mkdir -p "$NIX_BUILD_TOP" "$out"
+cd "$NIX_BUILD_TOP"
+```
 
 After this, the standard [build
 phases](https://nixos.org/nixpkgs/manual/#sec-stdenv-phases) can be
@@ -207,7 +203,8 @@ manually invoked and debugged
 ```bash
 eval "${unpackPhase:-unpackPhase}"
 cd "$sourceRoot"
-
+```
+```bash
 eval "${patchPhase:-patchPhase}"
 eval "${configurePhase:-configurePhase}"
 eval "${buildPhase:-buildPhase}"
@@ -229,7 +226,7 @@ Both this repository and nixpkgs-channel are regularly checked for
 updates by the [hydra server](https://hydra.sharcnet.ca).  If a newer
 version of either of these are found, the hydra server automatically
 clones them and attempts to build all the overlays defined in
-*pkgs/all-packages.nix* and temporary/all-temporary.nix* and a channel
+*pkgs/all-packages.nix* and *temporary/all-temporary.nix* and a channel
 tarball too.  The Compute Canada clusters monitor this process, and,
 if it succeeds, download the channel tarball and make it available as
 a new release.
@@ -240,9 +237,9 @@ This means deployment is as simple as doing
 git push
 ```
 
-waiting for a while (see the [hydra
-server](https://hydra.sharcnet.ca/) to check on progress), and then
-doing
+and waiting for a while (see the [hydra
+server](https://hydra.sharcnet.ca/) to check on progress).  Once it
+propagates to the clusters, anyone can update to it by running
 
 ```bash
 nix-channel --update