Hi Martin,
we'll be maintaining the developer docs and the upgrade.txt file in the mobile app source code with changes that may affect developers.
But, honestly, we have limited resources so we can't support or provide any additional documentation for people creating custom apps.
Regarding contributions, we haven't received much, but we've received more than expected. Developing for the mobile app usually requires a good understanding of Moodle and a good knowledge of the technologies used in the mobile app, and that's not easy.
In brief: the Mobile app documentation (both users and developers) will be keep updated but not tutorials or specific documentation for creating custom apps.