Rewrite workflow

[Daniel-Mietchen]

With better documentation than #113 and higher granularity for those parts that we are currently concerned with.

[Daniel-Mietchen]

I copied the text from #113 over to
https://github.com/wpoa/OA-signalling/blob/master/README.md#workflow
and added a bit more detail.

@difranco please ping me in this thread if you need further details.