Update README

Based on helping Amy to get it deployed to Heroku.
Use twitter-bootstrap-rails

Rather than having a static copy of bootstrap.min.css in the repo.

The site looks ever so slightly different with the newer version of bootstrap:
The header bar is grey rather than blank, and content is wider.
Use a narrower layout

I find this more visually appealing.
Tweak layout of bookmark

Move the domain, view and edit links to a new paragraph. I think this looks a
little better.