general: Miscellaneous documentation updates

- Add missing documentation for options and environment variables
- Rearrange definition and documentation of 'Options', 'Variables'
  and 'Aliases' in a consistent order

modules/homebrew/README.md

@@ -1,10 +1,10 @@
 Homebrew
 ========
 
-Defines Homebrew specific shell environment variables and aliases.
+Defines Homebrew specific environment variables and aliases.
 
-Environment Variables
----------------------
+Variables
+---------
 
 Execute the following to list the environment variables loaded in the shell:
 

modules/homebrew/init.zsh

@@ -11,7 +11,7 @@ if [[ "$OSTYPE" != (darwin|linux)* ]]; then
 fi
 
 #
-# Environmental Variables
+# Variables
 #
 
 # Load standard Homebrew shellenv into the shell session.