Closes #20090: update Doc/README and the error message in sphinx-build.py to make
it clear that any Python 3.x is not usable with the checked out Sphinx.
diff --git a/Doc/tools/sphinx-build.py b/Doc/tools/sphinx-build.py
index a446dfa..d3fe702 100644
--- a/Doc/tools/sphinx-build.py
+++ b/Doc/tools/sphinx-build.py
@@ -17,7 +17,7 @@
if sys.version_info[:3] < (2, 4, 0) or sys.version_info[:3] > (3, 0, 0):
sys.stderr.write("""\
-Error: Sphinx needs to be executed with Python 2.4 or newer (not 3.0 though).
+Error: Sphinx needs to be executed with Python 2.4 or newer (not 3.x though).
(If you run this from the Makefile, you can set the PYTHON variable
to the path of an alternative interpreter executable, e.g.,
``make html PYTHON=python2.5``).