Some changes to vimrc.

Add install.sh script.

To remove the symbolic link created in ~/.vimrc just do:

$ rm ~/.vimrc
or
$ unlink ~/.vimrc

Now after running ./install.sh anychanges made to ~/.vimrc will reflect
in this git repository and vice-versa.

Signed-off-by: Thiago Farina <tfarina@chromium.org>