Add usage info to readme

Author: brysgo

README.md

@@ -20,3 +20,31 @@ Copy or symlink:
 
 1. `bin/git_rails` into your executable `$PATH`
 2. `hooks/*` into your `.git/hooks/`
+
+### Usage
+
+#### Command
+
+After you checkout a branch, if you realize your migrations or gems are messed up from the switch, just run:
+
+`git_rails`
+
+This is the same as running:
+
+`git_rails ORIG_HEAD HEAD`
+
+If you know what ref you are coming from and it isn't `ORIG_HEAD` use:
+
+`git_rails [REF_YOU_JUST_CAME_FROM]`
+
+Or if you really know what you are doing and you want to pretend like you are on a different branch you can do:
+
+`git_rails [REF_YOU_CAME_FROM] [REF_YOU_ARE_GOING_TO]`
+
+Migrations that were added between `REF_YOU_CAME_FROM` and `REF_YOU_ARE_GOING_TO` that do not exist on your current `HEAD` will not be applied because they don't exist!!
+
+#### Hooks
+
+You shouldn't have to think about the hooks once they are installed. Just pull, checkout, and rebase as normal and they should work fine. If you find that `git_rails` hasn't fired when it should follow the command instructions to run it manually.
+
+Also, the hooks are optional, you can use `git_rails` without them!