Updated tested Python versions in README.

As per the GHA workflow files, only Python 3.8+ are tested.

Author: carltongibson

README.txt

@@ -61,7 +61,7 @@ we will link to it from this page.
 Python Versions
 ===============
 
-virtualenvwrapper is tested under Python 2.6 - 3.6.
+virtualenvwrapper is tested under Python 3.8 - 3.11.
 
 =======
 Support