Split repo documentation

The repo documentation targets both repo users (devs, test, api) and duniter users (api/manual, user). The duniter user documentation should be moved to duniter website repo and adapted for the public of duniter:

https://duniter.org/wiki/duniter-v2/ for technical public
https://duniter.org/wiki/g1v2/ for general public

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information