Home Assistant example contributing guidance, including modular, small as possible, and portable and reusable

[ericherman]

While not public code, the guidance for Home Assistant contributions may be worth including as an example:

https://developers.home-assistant.io/docs/creating_component_code_review/#4-communication-with-devicesservices

[ericherman]

Of special note is that that all extensions must exist in the public Python Package Index; this has the side-effect that any other python script should be able to use the extension, which makes the extensions modular, reusable, and portable by default -- any other python program -- not just Home Assistant -- can include and use the extension.