Update hdfs mkdir instructions to require a single command, rather than ...

Super minor possible change - instead of having two lines when creating /data/airline within hdfs, hdfs's mkdir will automatically create higher-level directories. So there is no need for a separate command to create /data within hdfs. I included a comment to make it clear though.

http://hadoop.apache.org/docs/r0.18.3/hdfs_shell.html#mkdir confirms this:
" mkdir

Usage: hadoop fs -mkdir <paths>

Takes path uri's as argument and creates directories. The behavior is much like unix mkdir -p creating parent directories along the path. "

I thought making a quick pull request might be more convenient than sending this via email, and as practice for pull requests.