Create a "roadmap" that gives a structured overview of what is there, what is missing, in which order things could be done

[fingolfin]

E.g. it could document things like "we have code for black box SLn recognition, it just is not hooked up" (see #59).

Or "There is code for recogntion of classical groups in natural rep; see PR #330 for SL_n part, the rest is also out there and needs to be added, point of contact for this is Max Horn"

etc. etc.

I.e. a document (section in the manual) that allows seeing this at once glance, without having to dig through 100+ issues.