mention the repo packages in the main readme

[devoncarew]

Description

• mention the repo packages in the main readme

Related Issues

Checklist

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• [x] I read the Contributor Guide and followed the process outlined there for submitting PRs.
• [x] My PR includes unit or integration tests for all changed/updated/fixed behaviors (See Contributor Guide).
• [x] All existing and new tests are passing.
• [x] I updated/added relevant documentation (doc comments with ///).
• [x] The analyzer (melos run analyze) does not report any problems on my PR.
• [x] I read and followed the Flutter Style Guide.
• [x] I signed the CLA.
• [x] I am willing to follow-up on review comments in a timely manner.

Breaking Change

Does your PR require plugin users to manually update their apps to accommodate your change?

• [ ] Yes, this is a breaking change.
• [x] No, this is not a breaking change.

[devoncarew]

cc @craiglabenz