[hibernate-dev] Compatibility Considerations wiki

[Steve Ebersole]

There was a discussion in regards to our view on backwards compatibility in
reference to HHH-9316.  I realized that we talk about this amongst
ourselves, but that I have never written these down.  So I did that:

https://github.com/hibernate/hibernate-orm/wiki/Compatibility-Considerations

This is a first draft.  Let me know what you think.