Where the documentation for self-hosting (docker) ?

Currently there is no documentation. The best example you can find here:

https://github.com/nhost/nhost/tree/main/examples/docker-compose

The docker-compose is pretty self-explanatory, though you will have to tweak with the traefik configuration a bit to make sure it works correctly

I suggest just deploying individual services if you need to self-host, for example I'm running hasura-auth on fly-io (1gb vm) and you can both deploy the compose, the dockerfile, and or the bundle of the app itself