README: add Python versions badge
# Plex-Trakt-Sync
+![Python Versions][python-versions-badge]
+
This project adds a two-way-sync between trakt.tv and Plex Media Server. It
requires a trakt.tv account but no Plex premium and no Trakt VIP subscriptions,
unlike the Plex app provided by Trakt.
+[python-versions-badge]: https://img.shields.io/badge/python-3.6%20%7C%203.7%20%7C%203.8%20%7C%203.9-blue
+
## Features
- Media in Plex are added to Trakt collection
