docs: add Omarchy plugin installation

[erzz]

Summary

• document installation of the CodeBurn Omarchy plugin
• link to the Omarchy plugin page

Validation

• npm run build
• git diff --check

[iamtoruk]

Reviewed — and reviewed the plugin repo itself too: clean script (whitelisted args, pinned package, graceful fallbacks), consumes the public menubar-json payload exactly as the add-only contract intends. This is precisely the kind of ecosystem integration we hoped that contract would enable — thank you for building it.

One small ask before merge: add a sentence marking it community-maintained so support expectations are clear, e.g.:

Community-maintained by @erzz — issues and feature requests go to erzz/omarchy-codeburn.

(Heads-up for your side: 0.9.21 lands soon; the payload changes are strictly add-only, so your pinned 0.9.20 and an upgraded CLI both keep working unchanged.)