Add a TODO about batching events

lib/crypto-algorithms/megolm.js

@@ -131,6 +131,12 @@ MegolmEncryption.prototype._ensureOutboundSession = function(room) {
                 var txnId = txnBase + (txnCtr++);
 
                 // TODO: send an OOB message. for now, send an in-band message.
+
+                // TODO: aggregate the messages into batches. If we make a
+                // separate request for each message, we will get rate-limited.
+                // On the other hand, we can't just send them in one big batch,
+                // because we'll hit the event size limit.
+
                 var path = utils.encodeUri(
                     "/rooms/$roomId/send/m.room.encrypted/$txnId", {
                         $roomId: self._roomId,