SingleCluster.html instructions are ordered incorrectly

I was going over the pesudo distributed cluster instructions at

https://hadoop.apache.org/docs/stable/hadoop-project-dist/hadoop-common/SingleCluster.html#Pseudo-Distributed_Operation

The smoke test instructions direct you to execute a mapreduce job

  $ bin/hadoop jar share/hadoop/mapreduce/hadoop-mapreduce-examples-3.3.6.jar grep input output 'dfs[a-z.]+'

but at this point Yarn hasn't been started, the instructions for that are in the next section.

Switch the YARN setup section and the smoke test section.