Link to plain text PEPs for 'Page Source' (#4561)

Author: StanFromIreland

pep_sphinx_extensions/pep_theme/templates/page.html

@@ -55,7 +55,7 @@ <h2>Contents</h2>
             {{ toc }}
             <br>
             {%- if not pagename.startswith(("pep-0000", "topic")) %}
-            <a id="source" href="https://github.com/python/peps/blob/main/peps/{{pagename}}.rst">Page Source (GitHub)</a>
+            <a id="source" href="https://github.com/python/peps/blob/main/peps/{{pagename}}.rst?plain=1">Page Source (GitHub)</a>
             {%- endif %}
         </nav>
         {%- endif %}