update prezto

.zprezto/modules/homebrew/README.md

@@ -1,7 +1,16 @@
 Homebrew
 ========
 
-Defines Homebrew aliases.
+Defines Homebrew specific environment variables and aliases.
+
+Variables
+---------
+
+Execute the following to list the environment variables loaded in the shell:
+
+```sh
+brew shellenv
+```
 
 Aliases
 -------
@@ -20,12 +29,9 @@ Aliases
 ### Homebrew Cask
 
   - `cask` is aliased to `brew cask`.
-  - `caskc` cleans up old cached downloads.
-  - `caskC` cleans up all cached downloads.
   - `caski` installs a cask.
   - `caskl` lists installed casks.
   - `casko` lists casks which have an update available.
-  - `casks` searches for a cask.
   - `caskx` uninstalls a cask.
 
 Authors