Add a new DNF tab to release pages

This tab gives instructions for setting up the new Artifactory rpm
repository so people can get daffodil updates using DNF for RPM-based
distros

DAFFODIL-2513
diff --git a/site/_layouts/release.html b/site/_layouts/release.html
index c01ac78..40aa6ba 100644
--- a/site/_layouts/release.html
+++ b/site/_layouts/release.html
@@ -31,6 +31,7 @@
       <li class="active"><a data-toggle="tab" href="#download">Download</a></li>
       <li><a data-toggle="tab" href="#maven">Maven</a></li>
       <li><a data-toggle="tab" href="#sbt">SBT</a></li>
+      <li><a data-toggle="tab" href="#rpm">DNF</a></li>
     </ul>
     <div class="tab-content">
       <div id="download" class="tab-pane fade in active">
@@ -101,6 +102,29 @@
 {% endunless %}
 {% endhighlight %}
       </div>
+      <div id="rpm" class="tab-pane fade">
+Create the file <code>/etc/yum.repos.d/apache-daffodil.repo</code> with the following content:
+
+<div style="padding: 10px 15px;">
+{% highlight ini %}
+[apache-daffodil]
+name=Apache Daffodil
+baseurl=https://apache.jfrog.io/artifactory/daffodil-rpm/
+enabled=1
+gpgkey=https://downloads.apache.org/daffodil/KEYS
+gpgcheck=1
+repo_gpgcheck=0
+{% endhighlight %}
+</div>
+
+Run the folllowing command:
+
+<div style="padding: 10px 15px;">
+{% highlight text %}
+sudo dnf install apache-daffodil
+{% endhighlight %}
+</div>
+      </div>
     </div>
   </div>
 </div>