Move README.md → README so that it gets included in packages by setuptools.

 * CHANGE the "Translations" section to accurately reflect required steps for
   updateing .pot files with strings which are newly added to BridgeDB's
   source code, as well as instructions for getting finished translations from
   gitweb.torproject.org/translations.git.
 * FIX a couple typos in the README.
Also remove the "bridge" prefix from returned pluggable transport lines.