Create HelloWorld.md

Supposed to push this from local repo, but git is borked on my PC.  Known issue: https://github.com/msysgit/git/issues/200

This is a workaround so I can 'complete' the Data Scientist's Toolbox course project.

Is just a nasty workaround box-tick however.  I really need git working for the rest of the course... hope the msysGit folk come up with something.