* You can start it as usual, `.env` file is automatically used.
* IMHO easier and cleaner to configure.
* Also removed the `<host>` as it makes this not-runnable out-of-the-box. I need this for https://github.com/Ravinou/borgwarehouse/pull/69 and this was the initial idea of making this PR.
* The `${:?}` syntax is a bash-like thing to produce a proper error message if the variable is not provided.
I checked the setup should basically start (just got a permission error as the UID/GID is wrong).