HDFS-5625. Add documentation example for setting a default ACL. Contributed by Chris Nauroth.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/HDFS-4685@1567422 13f79535-47bb-0310-9956-ffa450edef68

hadoop-common-project/hadoop-common/src/site/apt/FileSystemShell.apt.vm

@@ -444,6 +444,8 @@ setfacl
 
       * <<<hdfs dfs -setfacl -R -m user:hadoop:r-x /dir>>>
 
+      * <<<hdfs dfs -setfacl -m default:user:hadoop:r-x /dir>>>
+
    Exit Code:
 
    Returns 0 on success and non-zero on error.