Update docs for new package registry contributions

[tadasant]

Follow on to PR #350, we should update this contributor documentation: https://github.com/modelcontextprotocol/registry/blob/main/docs/new_package_registry.md

Not urgent, but I think a likely question we'll get as folks start using the Registry and realize their favorite package registry is not supported yet.

[domdomegg]

@claude can you take a stab at this?

[claude]

Claude finished @domdomegg's task —— View job • claude/issue-361-20250905-1317 • Create PR ➔

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Updated package registry contribution docs ✅

I've successfully updated the documentation for new package registry contributions following PR #350.

Todo List:

• Read current docs/new_package_registry.md file
• Review PR Add registry validators #350 to understand what changes were made
• Update the documentation accordingly
• Commit and push changes
• Provide PR creation link

Key changes from PR #350:

• Added registry validators for: npm, pypi, nuget, oci, mcpb
• New validation system requires specific metadata in packages to prevent misattribution
• Each registry type has different validation requirements

Documentation Updates Made:

• Added note about new validation requirements from PR Add registry validators #350
• Updated prerequisites to include validation mechanism requirement
• Added step to implement registry validator in the contribution process
• Added validation examples section showing how existing registries work