Fix the sys.path set up to point to the current working copy of review
board. Without this, the build of docs.db fails with:

ImportError: Could not import settings 'reviewboard.settings'

Also add the GitHub hosting service referenced in initial_data.json. Without
this, the build fails with:

CRITICAL:root:Resource "<class
'reviewboard.webapi.resources.hosting_service.HostingServiceResource'>"
requires objects in the database

make html now works. Didn't before this.