Update criteria

[jdebacker]

This PR updates the PSL criteria per changes voted on by the Leadership Council on 2022-01-22. They are:

• Change mandatory criteria 4 to read, "Include unit tests and ensure that the source code passes the tests."
• Add to the recommended criteria: "Add a "psl-cataloged" tag to the About section of the project's GitHub repository."
• Add to the recommended criteria: "Follow standard GitHub workflow practices, such as GitHub flow." Follow a standard contributor workflow, such as GitHub flow."
• Add to the recommended criteria: "Include continuous integration tests to ensure that tests are passing for proposed changes in pull requests and to document publicly that all unit tests are passing."

[jdebacker]

@Peter-Metz @MattHJensen Can you review and merge if ok?