Add docs

[benwainwright]

In order to be compliant with

• https://developers.home-assistant.io/docs/core/integration-quality-scale/rules/docs-actions/
• https://developers.home-assistant.io/docs/core/integration-quality-scale/rules/docs-high-level-description
• https://developers.home-assistant.io/docs/core/integration-quality-scale/rules/docs-installation-instructions
• https://developers.home-assistant.io/docs/core/integration-quality-scale/rules/docs-removal-instructions

I think documentation needs to be added to the home assistant documentation website: https://github.com/home-assistant/home-assistant.io