README.md: Python 3.11 is ok

Author: Matthias Koeppe

README.md

@@ -201,7 +201,7 @@ in the Installation Guide.
       more details.
 
     - Python 3.4 or later, or Python 2.7, a full installation including
-      `urllib`; but ideally version 3.9.x, or 3.10.x, which
+      `urllib`; but ideally version 3.9.x, 3.10.x, or 3.11.x, which
       will avoid having to build Sage's own copy of Python 3.
       See [build/pkgs/python3/SPKG.rst](build/pkgs/python3/SPKG.rst)
       for more details.