Add migration guide from 2019.02.06-1 to 2020.07.12-1

[Limess]

NOTE: Following upstream changes, Orchestra no longer includes the explain string in the thrown exception. In your applications, catch exceptions and output your own explain strings using the explain data in the exception. I recommend Expound, since it works well and is explicitly tested to do so with Orchestra.

This seems like a very sensible change. It would be incredibily useful if a plug-and-play example was provided in the README as to how to catch an orchestra exception and get the old behaviour using that exception as this seems to be a very common case.

[jeaye]

Sounds good, @Limess. I'll get that into the readme.

[vemv]

Hi @jeaye , any luck with this?

I recently had some trouble adapting Expound into a vanilla application using Orchestra. Currently getting both to get along together seems less documented than ideal.

Which would be odd for such a common use case.

Cheers - V