Add link to PSF in footer (#4439)

Author: azeemansar

warehouse/templates/base.html

@@ -284,7 +284,7 @@ <h2>Using PyPI</h2>
           <br>
           <a href="https://donate.pypi.org">Donate today!</a>
         </p>
-        <p>© {{ now()|format_date('yyyy') }} Python Software Foundation</p>
+        <p>© {{ now()|format_date('yyyy') }} <a href="https://www.python.org/psf/">Python Software Foundation</a></p>
       </div>
 
       <div class="centered hide-on-desktop">