update Sonarr or Radarr instructions

src/Jackett.Common/Content/index.html

@@ -75,6 +75,7 @@
                 <li>Go to <b>Settings > Indexers > Add > Torznab > Custom</b>.</li>
                 <li>Click on the indexers corresponding <button type="button" class="btn btn-xs btn-info">Copy Torznab Feed</button> button and paste it into the Sonarr/Radarr <b>URL</b> field.</li>
                 <li>For the <b>API key</b> use <b class="api-key-text"></b>.</li>
+                <li>Configure the correct category IDs via the <b>(Anime) Categories</b> options. See the Jackett indexer configuration for a list of supported categories.</li>
             </ol>
             <h4>Adding a Jackett indexer in CouchPotato</h4>
             <ol>