Add usage

README.md

@@ -2,5 +2,19 @@
 
 Here you'll find alternate versions of Casks for the homebrew-cask project.
 
+# Usage
+
+After you install homebrew-cask, run the following command:
+
+```sh
+$ brew tap caskroom/versions
+```
+
+You can now install alternate versions of Casks.
+
+```sh
+$ brew cask install iterm2-beta
+```
+
 ## License
 Code is under the [BSD 2 Clause (NetBSD) license](https://github.com/caskroom/homebrew-versions/blob/master/LICENSE)