Add documentation

[alerque]

There don't appear to be any vim-docs included in the plugin. At some point this should get it's own help page formatted for the internal help viewer.

[fmoralesc]

Right. Since the functionality was so limited, I thought the README was enough, but offline help seems like a good idea.

[alerque]

Ya I for one don't want to have to go fish up a README when I forget how to use plugins I've already installed! This isn't urgent, but it would be an easy thing for anybody to contribute with only a modicum of vim plugin experience. Hence the issue report ;-) Just a todo-list item.