add CHANGES_HDFS-5535.txt.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/HDFS-5535@1555023 13f79535-47bb-0310-9956-ffa450edef68

hadoop-hdfs-project/hadoop-hdfs/CHANGES_HDFS-5535.txt

@@ -0,0 +1,4 @@
+HDFS-5535 subtasks:
+
+    HDFS-5496. Make replication queue initialization asynchronous. (Vinay via
+    jing9)