Yes we have Docs!!!!

Guys, I took some time to improve our docs and came up with this http://fgrehm.viewdocs.io/vagrant-cachier~docs

I did my best to make things easier to understand and I'd **love** some feedback about it :smiley: 

On a side note, I've also documented some "gotchas" along the way like the issue with `bundle install --deployment` and the fact that the rvm bucket need some tweaking to provisioning scripts to work and also wrote down some notes I had about how people can help us out to implement support for new buckets.

Closes GH-56

/cc @mindreframer @cromulus @fh @gimler @laggyluke @patcon @tmatilai