Clarify the comment about setting the PYTHON variable for the Doc Makefile.
diff --git a/Doc/tools/sphinx-build.py b/Doc/tools/sphinx-build.py
index 8c9331e..e19b10a 100644
--- a/Doc/tools/sphinx-build.py
+++ b/Doc/tools/sphinx-build.py
@@ -13,9 +13,10 @@
if sys.version_info[:3] < (2, 5, 0):
print >>sys.stderr, """\
-Error: Sphinx needs to be executed with Python 2.5 or newer.
+Error: Sphinx needs to be executed with Python 2.5 or newer
(If you run this from the Makefile, you can set the PYTHON variable
-to the path of an alternative interpreter executable.)
+to the path of an alternative interpreter executable, e.g.,
+``make html PYTHON=python2.5``).
"""
sys.exit(1)