[skip ci]Add comment for rocksmq reader (#12898)

Signed-off-by: fishpenguin <kun.yu@zilliz.com>

internal/util/rocksmq/client/rocksmq/reader_impl.go

@@ -74,6 +74,7 @@ func (r *reader) HasNext() bool {
 	return r.c.server.HasNext(r.topic, r.name, r.startMessageIDInclusive)
 }
 
+// Close close the reader and stop the blocking reader
 func (r *reader) Close() {
 	r.c.server.CloseReader(r.topic, r.name)
 }