update social media links

Author: AllinCottrell

doc/website/template/index_pat.html

@@ -86,6 +86,18 @@
  </td>
 </tr>
 
+<tr>
+  <td><p>
+    <!-- rel="me" attribute required for account verification of Mastodon account -->
+    <a href="https://econtwitter.net/@gretl" rel="me" target="_blank">
+      <img src="https://upload.wikimedia.org/wikipedia/commons/4/48/Mastodon_Logotype_%28Simple%29.svg" alt="Mastodon" style="width: 20px; height: 20px; vertical-align: middle;">
+      Follow us on Mastodon
+  </a>
+  </p>
+  </td>
+</tr>
+
+
     </table>
       </td>
 
@@ -345,7 +357,7 @@ <h2><a name="git">Git access and browsing</a></h2>
 <h2><a name="ack">Acknowledgements</a></h2>
 
 <p>First of all, thanks to Ramu Ramanathan (1936-2013). Ramanathan was
-Professor of Economics at UCSD and author of 
+Professor of Economics at UCSD and author of
 <a href="http://econ.ucsd.edu/~rramanat/embook5.htm"> <i>Introductory
 Econometrics</i></a>. Gretl's origins lie in Ramanathan's
 open-sourcing of the C code for his econometrics program "ESL".</p>