YARN-2577. Clarify ACL delimiter and how to configure ACL groups only (Mikos Christine via aw)

hadoop-yarn-project/CHANGES.txt

@@ -226,6 +226,9 @@ Release 2.6.0 - UNRELEASED
     YARN-1959. Fix headroom calculation in FairScheduler. 
     (Anubhav Dhoot via kasha)
 
+    YARN-2577. Clarify ACL delimiter and how to configure ACL groups only
+    (Miklos Christine via aw)
+
   OPTIMIZATIONS
 
   BUG FIXES

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-site/src/site/apt/FairScheduler.apt.vm

@@ -405,6 +405,9 @@ Queue Access Control Lists (ACLs)
   that queue or in the ACL of any of that queue's ancestors. So if queue2
   is inside queue1, and user1 is in queue1's ACL, and user2 is in queue2's
   ACL, then both users may submit to queue2.
+
+  <<Note:>> The delimiter is a space character. To specify only ACL groups, begin the 
+  value with a space character. 
   
   The root queue's ACLs are "*" by default which, because ACLs are passed down,
   means that everybody may submit to and kill applications from every queue.