docs: Moving release note to docs/source, so it is visible on ndnSIM website

Change-Id: I211ac6e3a723a9b5f7310741334818af7fac2b19
diff --git a/docs/source/_templates/indexcontent.html b/docs/source/_templates/indexcontent.html
index 4b07a6e..6a44ca6 100644
--- a/docs/source/_templates/indexcontent.html
+++ b/docs/source/_templates/indexcontent.html
@@ -56,6 +56,7 @@
   <p><strong>Meta information:</strong></p>
   <table class="contentstable" align="center"><tr>
     <td width="50%" valign="top">
+      <p class="biglink"><a class="biglink" href="{{ pathto("RELEASE_NOTES") }}">Release Notes</a></p>
       <p class="biglink"><a class="biglink" href="{{ pathto("meta/bugs") }}">Reporting bugs</a></p>
       <p class="biglink"><a class="biglink" href="{{ pathto("meta/about") }}">About the documentation</a></p>
     </td><td width="50%" valign="top">