Add note about removing options

[agners]

Proposed change

SSIA

Type of change

• Document existing features within Home Assistant
• Document new or changing features which there is an existing pull request elsewhere
• Spelling or grammatical corrections, or rewording for improved clarity
• Changes to the backend of this documentation
• Removed stale or deprecated documentation

Additional information

• This PR fixes or closes issue: relates to Supervisor logs warnings for add-on options that have been removed supervisor#4644
• Link to relevant existing code or pull request:

[home-assistant]

Please take a look at the requested changes, and use the Ready for review button when you are done, thanks 👍

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[frenck]

Thanks, @agners 👍

../Frenck