add an example that runs wordcount over file datasets

simple example to read and write files. 
- a service that can upload/download files
- a mapreduce that reads/writes the same files, with runtime arguments to specify the paths

I am open to renaming this, if you have a better suggestion. 
Insert blank line and \<p> before \<ul>...and remove the \</ul> on this line. Add a trailing \</p>