HADOOP-18597. Simplify single node instructions for creating directories for Map Reduce. (#5305)

Signed-off-by: Ayush Saxena <ayushsaxena@apache.org>

hadoop-common-project/hadoop-common/src/site/markdown/SingleCluster.md.vm

@@ -157,8 +157,7 @@ The following instructions are to run a MapReduce job locally. If you want to ex
 
 4.  Make the HDFS directories required to execute MapReduce jobs:
 
-          $ bin/hdfs dfs -mkdir /user
-          $ bin/hdfs dfs -mkdir /user/<username>
+          $ bin/hdfs dfs -mkdir -p /user/<username>
 
 5.  Copy the input files into the distributed filesystem: