Make it clear that the `[awaiting ...]` labels are for the bots only.

[Mariatta]

The [awaiting ...] labels are meant to be automatically added by bedevere bot. Both miss-islington and bedevere rely on these labels in order to work properly, so it's like a contract between the two bots.

It would be great to clarify in the devguide that these labels should only be used by the bots and should not be manipulated manually.

Maybe it would also be great to refer to the state machine here: https://github.com/python/bedevere/blob/main/bedevere/stage.py#L7
(and render the state machine too perhaps?)

[hugovk]

Adding something to the description like "For bot use only" would help as well, it would show in the dropdown when triagers are selecting labels.

[ezio-melotti]

(and render the state machine too perhaps?)

I created python/bedevere#500 to add a render of the state machine to the README of bedevere.

I'll fix the rest of the issue as part of #930.