HDFS-12536. Add documentation for getconf command with -journalnodes option. Contributed by Bharat Viswanadham.

hadoop-hdfs-project/hadoop-hdfs/src/site/markdown/HDFSCommands.md

@@ -116,6 +116,7 @@ Usage:
        hdfs getconf -namenodes
        hdfs getconf -secondaryNameNodes
        hdfs getconf -backupNodes
+       hdfs getconf -journalNodes
        hdfs getconf -includeFile
        hdfs getconf -excludeFile
        hdfs getconf -nnRpcAddresses
@@ -126,6 +127,7 @@ Usage:
 | `-namenodes` | gets list of namenodes in the cluster. |
 | `-secondaryNameNodes` | gets list of secondary namenodes in the cluster. |
 | `-backupNodes` | gets list of backup nodes in the cluster. |
+| `-journalNodes` | gets list of journal nodes in the cluster. |
 | `-includeFile` | gets the include file path that defines the datanodes that can join the cluster. |
 | `-excludeFile` | gets the exclude file path that defines the datanodes that need to decommissioned. |
 | `-nnRpcAddresses` | gets the namenode rpc addresses |