Add initial content to README.md

[sethwv]

Description

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How was it tested?

Checklist

Please check every item before marking this PR as ready for review. Unchecked items will be flagged during review.

• I have read the CONTRIBUTING.md in full
• I agree to the Contributor License Agreement
• I understand — line by line — every change in this PR and can explain it if asked
• This PR targets the dev branch
• Backend: migrations are included if any models were changed
• Backend: new API endpoints appear correctly in the OpenAPI schema
• Frontend: ESLint and Prettier pass cleanly (npm run lint, npm run format)
• Tests are included for new functionality
• Existing tests still pass
• No console.log, print(), debug statements, or commented-out code is left in the diff
• I have not reformatted or refactored code outside the scope of this change

[dispatcharr-issues-bot]

Please change your pull request to target the dev branch rather than main.