Copied it over to https://github.com/OpenLMIS/openlmis-auth/blob/master/DESIGN.md, with a link from the README. Had to put in the formatting manually.

@Chongsun Ahn Okay, I'm done with all my revisions. Please give it a quick read to make sure it is factually correct: https://openlmis.atlassian.net/wiki/display/OP/Auth+Design

I suggest we leave this in the Wiki for now. We have a lot of documentation in the Wiki that should move to ReadTheDocs eventually, but we don't yet have any structure or organization for that. I hope to work on that before our 3.0 release, but I don't think it should hold up this ticket (let me know if you disagree).

Draft is here: https://openlmis.atlassian.net/wiki/display/OP/Auth+Design

@Brandon Bowersox-Johnson If you can determine that it can be moved to something like ReadTheDocs now, then let's move it. But if we'll need to make significant changes first, let's make the changes and then move it over.