feat(docs): Add docs for Appset UI

[pjiang-dev]

Checklist:

• Either (a) I've created an enhancement proposal and discussed it with the community, (b) this is a bug fix, or (c) this does not need to be in the release notes.
• The title of the PR states what changed and the related issues number (used for the release note).
• The title of the PR conforms to the Title of the PR
• I've included "Closes [ISSUE #]" or "Fixes [ISSUE #]" in the description to automatically close the associated issue.
• I've updated both the CLI and UI to expose my feature, or I plan to submit a second PR with them.
• Does this PR require documentation updates?
• I've updated documentation as required by this PR.
• I have signed off all my commits as required by DCO
• I have written unit and/or e2e tests for my change. PRs without these are unlikely to be merged.
• My build is green (troubleshooting builds).
• My new feature complies with the feature status guidelines.
• I have added a brief description of why this PR is necessary and/or what this PR solves.
• Optional. My organization is added to USERS.md.
• Optional. For bug fixes, I've indicated what older releases this fix should be cherry-picked into (this may or may not happen depending on risk/complexity).

[bunnyshell]

🔴 Preview Environment stopped on Bunnyshell

See: Environment Details | Pipeline Logs

Available commands (reply to this comment):

• 🔵 /bns:start to start the environment
• 🚀 /bns:deploy to redeploy the environment
• ❌ /bns:delete to remove the environment

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 64.48%. Comparing base (f7ea5bc) to head (f96a1bb).
⚠️ Report is 13 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #27910      +/-   ##
==========================================
+ Coverage   64.39%   64.48%   +0.09%     
==========================================
  Files         422      422              
  Lines       57829    58086     +257     
==========================================
+ Hits        37239    37457     +218     
- Misses      17089    17108      +19     
- Partials     3501     3521      +20     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.