Start moving internal documentation to /docs

Tasks

• start a wiki
• move some low-hanging fruit(s) from internal docs to it (cross-ref new location from old)
• figure out and document a way to dump wiki into a tree of *.md-files in /docs in this repo. (my first idea, possibly no fun or invalid: write a small shell script that pulls everything from the wiki, overwrites the working copy with the changes, and commits this to a branch docs-<timestamp>.)
• (optional?) figure out a way to sync /docs back into wiki, should somebody prefer to work there.

for a light-weight process to keep wiki and /docs in sync: we can add "call that script" to the release procedure.

Start by reviewing the existing wiki, internal documentation, and the /docs directory. Define the scope for the initial migration, cross-reference moved pages from their old locations, and document the wiki-to-*.md export process. Done means the selected documentation is migrated and the release procedure records how to keep the locations in sync.