Generalized install step, esp. for Android users

I use git, emacs, and vim on my Android phone. In this environment, git has trouble with `https://...` repos, but fortunately it handles `git@github...` URLs fine.

README.md

@@ -9,7 +9,7 @@
 1. Setup [Vundle]:
 
      ```
-     $ git clone https://github.com/gmarik/vundle.git ~/.vim/bundle/vundle
+     $ git clone git@github.com:gmarik/vundle.git ~/.vim/bundle/vundle
      ```
 
 2. Configure bundles: