Add channel's RSS link to the settings tab.

frontends/ycdl_flask/templates/channel.html

@@ -270,6 +270,8 @@ https://stackoverflow.com/a/35153397
         <button id="set_queuefile_extension_button" class="button_with_spinner" onclick="return set_queuefile_extension_form();">Set extension</button>
     </div>
 
+    <a href="https://www.youtube.com/feeds/videos.xml?channel_id={{channel.id}}">Channel RSS</a>
+
     <button class="red_button button_with_confirm"
     data-prompt="Delete channel and all videos?"
     data-onclick="return delete_channel_form();"