New cmd_help needs to be built for 'tox -e doc'

Author: nedbat

tox.ini

@@ -60,7 +60,10 @@ basepython = {env:COVERAGE_PYTHON}
 # return.
 deps =
     -r doc/requirements.pip
+whitelist_externals =
+    make
 commands =
+    make cmd_help
     python doc/check_copied_from.py doc/*.rst
     doc8 -q --ignore-path 'doc/_*' doc CHANGES.rst README.rst
     sphinx-build -b html -aqE doc doc/_build/html