add note about populate + match in chatc

src/controllers/groups.js

@@ -121,16 +121,17 @@ api.postChat = function(req, res, next) {
   }
 
   async.series([
-    function(cb){
-      group.save(cb)
-    },
+    function(cb){group.save(cb)},
     function(cb){
       Group.findById(group._id).populate('members', partyFields).exec(cb);
     }
   ], function(err, results){
     if (err) return res.json(500, {err:err});
+
+    // TODO This is less efficient, but see https://github.com/lefnire/habitrpg/commit/41255dc#commitcomment-4014583
     var saved = results[1];
     saved.members = _.filter(saved.members, function(m){return m._id != user._id});
+
     res.json(saved);
   })
 }