diff --git a/README.md b/README.md
index 4634ded..f8a0d63 100644
--- a/README.md
+++ b/README.md
@@ -1,12 +1,11 @@
 # Overview
 
 This package contains a collection of Nix expressions created by
-SHARCNET staff for various software packages.  Once copied or linked
-into your *~/.nix-defexpr* directory they will allow you to install
-the associated package into your Nix environment.
+SHARCNET staff for various software packages.  You can use them to
+install the associated packages into your Nix environment.
 
-These directions assume you have loaded the Nix module (this enabes
-your Nix environment and makes the various Nix commands avaialble)
+These directions assume you have loaded the Nix module (this enables
+your Nix environment and makes the various Nix commands available)
 
 
 ```sh
@@ -30,31 +29,24 @@ cd ~/nix-nixpkgs-sharcnet
 git pull
 ```
 
-## Installing an expression
-
-To use any of the provided Nix expressions, you need to copy it to or
-link it into your *~/.nix-defexpr* directory (replace *package.nix*
-with the name of the Nix expression you wish to use)
-
-```sh
-ln -s ../nix-nixpkgs-sharcnet/package.nix ~/.nix-defexpr/
-
-```
-
-Using a symbolic link has the advantage that it automatically gets
-updated whenever you update *~/nix-nixpkgs-sharcnet*.
-
 # Using an expression
 
-Once you have the expression in your *~/.nix-defexpr* you can use the
-`nix-env` command to install (or update) the associated package in
-your Nix environment.
+Once you have a copy of the expressions you can use `nix-env` to
+install, update, or remove them from your environment.
 
-## Installing and updating
 
-To install or update the associated package (replace *package* with
-the base name of the Nix expression file you copied to
-*~/.nix-defexpr*)
+## Installing an expression
+
+To install (or update) a package pass the corresponding file (replace
+*package.nix* in what follows) to `nix-env` using the `--file` option
+
+```sh
+nix-env --install --file package.nix
+```
+
+You can also copy or symlink the file into your *~/.nix-defexpr*
+directory and then refer to it as a top-level attribute (replace
+*package* with the base name of the copied file)
 
 ```sh
 nix-env --install --attr package
@@ -63,7 +55,7 @@ nix-env --install --attr package
 ## Removing
 
 To remove a package you first need to figure out its name (generally,
-but not nessesarily, the same as the name of the Nix expression file)
+but not necessarily, the same as the name of the Nix expression file)
 
 ```sh
 nix-env --query