Comment override rule stuff

src/RoomNotifs.js

@@ -69,7 +69,11 @@ function setRoomNotifsStateMuted(roomId) {
         promises.push(cli.deletePushRule('global', 'room', roomRule.rule_id));
     }
 
-    // add an override rule to squelch everything in this room
+    // add/replace an override rule to squelch everything in this room
+    // NB. We use the room ID as the name of this rule too, although this
+    // is an override rule, not a room rule: it still pertains to this room
+    // though, so using the room ID as the rule ID is logical and prevents
+    // duplicate copies of the rule.
     promises.push(cli.addPushRule('global', 'override', roomId, {
         conditions: [
             {