implement "no devices" prompt for admin users to do first discover

Netdisco/share/views/index.tt

@@ -44,6 +44,19 @@
         <script type="text/javascript"> $('#nq').focus(); // set focus to navbar search </script>
         [% END %]
       </div>
+      [% IF vars.nodevices %]
+      <div class="hero-unit">
+        <h3>Initial Discovery</h3>
+        <p>You haven't discovered any devices yet.<p>
+        <p>Enter a network device name or IP to queue the first discovery:</p>
+        <form method="post" action="[% uri_for('/admin/discover') %]">
+          <div class="form-horizontal">
+            <input placeholder="Device hostname or IP" class="span4" name="device" type="text"/>
+            <button type="submit" class="btn btn-info">Discover</button>
+          </div>
+        </form>
+      </div>
+      [% END %]
     </div>
   </div>
 </div> <!-- /container -->