Update README.md

[rlfagan]

updating docs for supported branches

Overview

Provide an overview of this change. Describe the intent of this change, and how it implements that intent.

Example: This PR accomplishes X by doing Y.

Acceptance criteria

If this PR is successful, what impact does it have on the user experience?

Example: When users do X, Y should now happen.

Testing plan

How did you validate that this PR works? What literal steps did you take when manually checking that your code works?

Example:

1. Set up test case X.
2. Run command Y. Make sure Z happens.

This section should list concrete steps that a reviewer can sanity check and repeat on their own machine (and provide any needed test cases).

Risks

Highlight any areas that you're unsure of, want feedback on, or want reviewers to pay particular attention to.

Example: I'm not sure I did X correctly, can reviewers please double-check that for me?

References

Add links to any referenced GitHub issues, Zendesk tickets, Jira tickets, Slack threads, etc.

Example:

• ANE-123: Implement X.

Checklist

• I added tests for this PR's change (or explained in the PR description why tests don't make sense).
• If this PR introduced a user-visible change, I have updated relevant documentation.

[jssblck]

@rlfagan how did you validate that the named branches are supported in the equivalent meta-fossa branches?

Also, branches added to the support matrix for this repo must follow the precedent established in this repo, which is to give each supported Yocto branch its own meta-fossa branch with dedicated tests for that Yocto branch.

If you'd like us to implement this, please create tickets for branch support and work with the team to prioritize. For example a ticket to support Morty exists here; you could create a new ticket per branch or modify this ticket with all the branches for which you want us to add support.