Add link to Python glossary page at /doc/ (#1650)

Fixes #1620

Author: sk1122

templates/python/documentation.html

@@ -68,6 +68,7 @@ <h2 class="widget-title"><span aria-hidden="true" class="icon-versions"></span>P
                                     <li><a href="https://docs.python.org/3/c-api/index.html">Python/C API</a></li>
                                     <li><a href="https://docs.python.org/3/using/index.html">Using Python</a></li>
                                     <li><a href="https://docs.python.org/3/howto/index.html">Python HOWTOs</a></li>
+                                    <li><a href="https://docs.python.org/3/glossary.html">Glossary</a></li>
                                 </ul>
                             </li>
                             <li><a href="https://docs.python.org/3/search.html">Search the online docs</a></li>