Remove 'Community' section from README
Remove 'Community' section from README

The Mzalendo Users group is effectively dead, and there's no real value
in trying to bring it back to life. We _could_ suggest that people
discuss Pombola on the Poplus mailing list, but it's probably easiest
to just remove the section entirely for now.

mysociety/pombola,mysociety/pombola,mysociety/pombola,mysociety/pombola,mysociety/pombola,mysociety/pombola