about.html: Include citation to ICON and KONECT

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+.footnote li p:last-child {
+    margin-bottom: 0
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templates/about.html

@@ -58,18 +58,40 @@ active
 
       <p>When collecting data for this website, we made extensive use of
       the <a href="https://icon.colorado.edu">Index of Complex Networks
-      (ICON)</a> by the group
+      (ICON)</a><sup id="fnref:icon"><a class="footnote-ref"
+      href="#fn:icon">1</a></sup> by the group
       of <a href="http://tuvalu.santafe.edu/~aaronc">Prof. Aaron
       Clauset</a> at the University of Colorado Boulder, as well as
-      the <a href="http://konect.cc">KONECT</a> project, by Jérôme
-      Kunegis.
+      the <a href="http://konect.cc">KONECT</a>
+      project<sup id="fnref:konect"><a class="footnote-ref"
+      href="#fn:konect">2</a></sup>, by Jérôme Kunegis.
 
       <p>The dataset "tags" reflect in large part the taxonomy and graph
       attributes that have been compiled by
-      the <a href="https://icon.colorado.edu">ICON</a> project, as well
-      as the data descriptions themselves.
+      the <a href="https://icon.colorado.edu">ICON</a>
+      project<sup id="fnref:icon"><a class="footnote-ref"
+      href="#fn:icon">1</a></sup>, as well as the data descriptions
+      themselves.
       </p>
-      
+
+      <div class="footnote">
+        <hr />
+        <ol>
+          <li id="fn:icon">
+            <p>Aaron Clauset, Ellen Tucker and Matthias Sainz, "The
+            Colorado Index of Complex
+            Networks."  <a href="https://icon.colorado.edu/">https://icon.colorado.edu/</a>
+            (2016).&#160;<a class="footnote-backref" href="#fnref:icon"
+            title="Jump back to footnote 1 in the text">&#8617;</a></p>
+          </li>
+          <li id="fn:konect">
+            <p>Jérôme Kunegis. "KONECT – The Koblenz Network Collection." In Proc. Int. Conf. on World Wide Web Companion, pages 1343–1350, 2013. <a href="https://doi.org/10.1145/2487788.2488173">doi:10.1145/2487788.2488173</a>
+              &#160;<a class="footnote-backref" href="#fnref:konect"
+            title="Jump back to footnote 2 in the text">&#8617;</a></p>
+          </li>
+        </ol>
+      </div>
+
     </blockquote>
 
     <blockquote style="font-size: smaller">