Use vim's syntax for control key, e.g. <C-a> vs ^a.
Add instructions on adding ~/bin to $PATH.

We install the vim shim in ~/bin, and MA may not work well if that shim is not what is being used.
Merge pull request #120 from square/donovan/add-path-instructions

Add instructions on adding ~/bin to $PATH.
Merge branch 'master' into mine