Fix bullet list in catalog

[jiahaog]

Description

This list is broken on https://a2ui.org/concepts/catalogs/#freestanding-catalogs

I think the missing newline is the issue. Also use * for the bullet list since the rest of the file uses that but I don't think that affects rendering.

Pre-launch Checklist

• I signed the CLA.
• I read the Contributors Guide.
• I read the Style Guide.
• I have added updates to the CHANGELOG.
• I updated/added relevant documentation.
• My code changes (if any) have tests.

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[gemini-code-assist]

Code Review

This pull request fixes a broken bulleted list in the catalogs.md documentation by adding a required newline and making the list style consistent with the rest of the document. The change is correct and improves the readability of the documentation. I've added one comment to correct the list of available choices for the --version argument, which was incomplete.