Mention previous Coq versions (updated version of Hugo's PR#34)

pages/download.html

@@ -53,4 +53,24 @@
 </div><!-- frameworkcontent -->
 </div><!-- framework -->
 
+<div class="framework">
+<div class="frameworklabel">Previous and development versions of Coq </div>
+<div class="frameworkcontent">
+
+<p> The previous stable release of the Coq system is
+<a href="/coq-86">version 8.6</a>.
+</p>
+
+<p>The development version of Coq is <a href="https://github.com/coq/coq">browsable</a>
+and downloadable from our Git repository using command:
+<tt>git clone https://github.com/coq/coq.git</tt>.
+The daily level of stability of this version can be observed at the
+<a href="https://ci.inria.fr/coq/job/bench-clone-coq/">bench-clone-coq</a> site.
+</p>
+
+<p>Most of the previous versions of Coq are available <a href="/distrib/">here</a>.</p>
+
+</div>
+</div>
+
 <#include "incl/footer.html">