Update documented supported Python versions

Author: jordaneb

README.md

@@ -9,7 +9,7 @@ Asynchronous tasks are run via a *job queue*. This system is designed to support
 
 Supported and tested against:
 - Django 1.11 and 2.2
-- Python 3.7 and 3.8
+- Python 3.5, 3.6, 3.7 and 3.8
 
 This package may still work with older versions of Django and Python but they aren't explicitly supported.