consolidate documentation

[splitbrain]

Currently we have documentation at various places:

• [x] https://github.com/dokuwiki/translate.dokuwiki.org/blob/master/README.md
• [x] https://github.com/dokuwiki/translate.dokuwiki.org/blob/master/TODO
• [x] https://github.com/dokuwiki/translate.dokuwiki.org/wiki
• [x] https://www.dokuwiki.org/teams:translate-tool

This should be consolidated in one place (I think the github wiki is a good choice) and updated to reflect the current state.

[Klap-in]

Every thing moved to the GitHub wiki. Todos are now in the issue tracker.