CHANGES.txt: add HADOOP-11257

hadoop-common-project/hadoop-common/CHANGES.txt

@@ -396,6 +396,9 @@ Release 2.7.0 - UNRELEASED
 
     HADOOP-11173. Improve error messages for some KeyShell commands. (wang)
 
+    HADOOP-11257: Update "hadoop jar" documentation to warn against using it
+    for launching yarn jars (iwasakims via cmccabe)
+
   OPTIMIZATIONS
 
     HADOOP-11323. WritableComparator#compare keeps reference to byte array.