Update README (#883)

Author: raunc

README.md

@@ -492,7 +492,7 @@ The following table lists important methods for this API.
 |`consumer.disconnect()` | Disconnects from the broker. <br><br>The `disconnect()` method emits `disconnected` when it has disconnected. If it does not, the error will be passed through the callback. |
 |`consumer.subscribe(topics)` | Subscribes to an array of topics. |
 |`consumer.unsubscribe()` | Unsubscribes from the currently subscribed topics. <br><br>You cannot subscribe to different topics without calling the `unsubscribe()` method first. |
-|`consumer.consume(cb)` | Gets messages from the existing subscription as quickly as possible. This method keeps a background thread running to do the work. If `cb` is specified, invokes `cb(err, message)`. |
+|`consumer.consume(cb)` | Gets messages from the existing subscription as quickly as possible. If `cb` is specified, invokes `cb(err, message)`. <br><br>This method keeps a background thread running to do the work. Note that the number of threads in nodejs process is limited by `UV_THREADPOOL_SIZE` (default value is 4) and using up all of them blocks other parts of the application that need threads. If you need multiple consumers then consider increasing `UV_THREADPOOL_SIZE` or using `consumer.consume(number, cb)` instead. |
 |`consumer.consume(number, cb)` | Gets `number` of messages from the existing subscription. If `cb` is specified, invokes `cb(err, message)`. |
 |`consumer.commit()` | Commits all locally stored offsets |
 |`consumer.commit(topicPartition)` | Commits offsets specified by the topic partition |