Add new course instructions to README

[kaelynj]

We have a nice write-up on how to migrate courses while we were migrating platforms which contain useful instructions on how to add new course content to the documentation. We should incorporate what's written there into our own README.

https://gist.github.com/frankharkins/c6c04a0ed09a35f72f264774301c08e5

[kaelynj]

Hey @kcmccormibm, did you end up using this guide for adding the new course content? If so, would you be up for editing/finding a nice place in our README to put these instructions since its fresh in your mind?

[kcmccormibm]

@kaelynj Sorry I didn't see your tag earlier. Yes I can do that!