Adding bitbucket instructions

They instructions would also work for GitHub pages I believe, and I also believe they are simpler (at least it was for me).
Ack, sorry—this needs to be a H2, since the _Publish_ section below is also applicable.

I’d rename the _With GitHub Pages_ section to _With GitHub Pages or Bitbucket_, and rename the _Setup_ section above to _With GitHub Pages_. Now you can leave this header as-is.