Doc Revision: contributing

[markstur]

Summary of Requested Changes:
agentstack Contributing doc and contributing.md does not address legal contributing info or what a new committer needs to know. Seems like more of a developers doc and not a contributors doc. At least it should mention legal.

See beeai-framework which has a similar doc but at least has a legal section, but probably even better to link to the community contributing legal section.

This is an issue for both the docs contributing section and the CONTRIBUTING.md.

Requirements
Should mention license, copyright, DCO, sign-off...
Perhaps using a link to here

Task Checklist

• Contributing Guideline Compliance: I read and complied by "Documentation Contribution Guidelines" section of the Agent Stack project CONTRIBUTING.md guide.
• Snippet Test: Verified all code works in a fresh environment (fresh agent stack install and clean environment).
• Visual Preview: Checked formatting/layout via Mintlify.
• CLI Sync: Ran mise run agentstack-cli:docs (if applicable).
• Location: Updates placed in docs/development for go live during next release or both docs/development and docs/stable for urgent go live.

[markstur]

also suggested:

• hmm suggest making that more prominent at the top.. the difference between this contributing document and the existing
• something like.. This is the contributing guide for ____, additionally the repo has a `CONTRIBUTING.md