docs: add supported python versions

Merge pull request #44 from AbdallahAlhaddad/patch-1

Author: Ivelin Ivanov

README.md

@@ -64,6 +64,9 @@ Initial working prototype completed. PeerJS Python is now able to connect over W
 -  [x] Release initial version to PyPi.
 -  [ ] >90% code coverage with CI tests.
 -  [ ] Port media support.
+-  [x] support for python 3.7 & python 3.8
+-  [ ] support for python 3.9
+
 
 ## Code Examples