two different keys set the same key in .env for the leading `AIO_` prefix (quirk)

For an .env file
```
AIO_RUNTIME_AUTH=foo
AIO__RUNTIME_AUTH=bar
```

Both keys are effectively the same key `runtime.auth`
This will not be apparent to the user, and may just be a documentation issue.

`AIO_RUNTIME_AUTH` is processed as `runtime.auth`
`AIO__RUNTIME_AUTH` is processed as `.runtime.auth` (note the leading period). The leading period is split out when calling `setValue`.

## Fix:
Document that any .env vars that are prefixed by `AIO_` or `AIO__` are equivalent (one or two underscores). Anything more than two will be reflected as an underscore itself.

Start by locating the configuration documentation that explains .env variable names and the AIO_ prefix. Verify the documented examples against the described setValue behavior, then document that AIO_ and AIO__ are equivalent while additional underscores remain part of the key.

Written by the indexing model from the issue text.