Document hosting solution & deployment pipeline

[polymutex]

Originally posted by @Hugoo in https://github.com/walletbeat/walletbeat/issues/183#issuecomment-2990216683

idk if it is somewhere else in the code but it might be nice to document this in a .md file, just to explain flow, how to set the keys (GIT_SSH_AUTHENTICATION_KEY_PUBLIC )etc on the helios side. if someone else come, they can get the context

More generally, it would be useful to document the setup Walletbeat has so that other projects may replicate or improve upon it.