Post-migration cleanup

[MajorLift]

Tasks

• Transfer open issues from the source repo into the core monorepo using the Transfer issue feature.
  • If applicable, rename to include package name to provide better context when encountered in the core monorepo.
• For open PRs in the source repo, lock conversation (with no reason provided), and leave a comment requesting that authors reopen the PR in core with a link pointing to the discussion in the original PR.

This library has now been migrated into the [core monorepo](https://github.com/metamask/core/). This PR has been locked and this repo will be archived shortly. Going forward, releases of this library will only include changes made in the core repo.
- Please push this branch to core and open a new PR there.
- Optionally, add a link pointing to the discussion in this PR to provide context.

• Leave a note in the source repo's README announcing the migration and pointing to core.
  • Add migrated and archived notice to README #80

<table><tr><td><p align="center"><b>⚠️ PLEASE READ ⚠️</b></p><p align="center">This package has been migrated to our <a href="https://github.com/MetaMask/core"><code>core</code></a> monorepo, and this repository has been archived. Please note that all future development and feature releases will take place in the <a href="https://github.com/MetaMask/core"><code>core</code></a> repository.</p></td></tr></table>

• Archive the source repo to prevent any changes from being pushed to it going forward.

References

• See #1551 (comment) for context on the migration process.
• See #1079 (comment) for context on the migration initiative.