twrpme: add gitactivity changelog tag to device markdowns

Change-Id: I437a42c1b2ccd79b3f85ad0962c362680c28d171
diff --git a/_layouts/device.html b/_layouts/device.html
index ca40b86..3dd234a 100644
--- a/_layouts/device.html
+++ b/_layouts/device.html
@@ -10,6 +10,7 @@
 
   <article class="post-content">
     {{ content }}
+    {% if page.devicetree %} {{ page.devicetree | gitactivity }} {% endif %}
   </article>
 
 </div>