update tested python release info.

Author: rouilj

CHANGES.txt

@@ -8,8 +8,9 @@ Many entries without name were done by Richard Jones.
 
 **IMPORTANT** The v1.5.x releases of Roundup were the last to support
 Python v2.5 and v2.6.  Starting with the v1.6 releases of Roundup
-v2.7.2 or later are required to run newer releases of Roundup.  From v2.0
-onwards Python 3.4 and later are also supported.
+v2.7.2 or later are required to run newer releases of Roundup.
+Roundup 2.0 supports Python 3.4 and later. Roundup 2.1.0 supports
+python 3.6 or newer (3.4/3.5 might work, but they are not tested).
 
 2022-yy-zz 2.2.0