Add community-projects reference document (#569)

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## Motivation and Context
<!-- Why is this change needed? What problem does it solve? -->
The following adds a doc to reference community projects.
 
## How Has This Been Tested?
<!-- Have you tested this in a real application? Which scenarios were
tested? -->

## Breaking Changes
<!-- Will users need to update their code or configurations? -->

## Types of changes
<!-- What types of changes does your code introduce? Put an `x` in all
the boxes that apply: -->
- [ ] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to change)
- [x] Documentation update

## Checklist
<!-- Go over all the following points, and put an `x` in all the boxes
that apply. -->
- [ ] I have read the [MCP
Documentation](https://modelcontextprotocol.io)
- [ ] My code follows the repository's style guidelines
- [ ] New and existing tests pass locally
- [ ] I have added appropriate error handling
- [ ] I have added or updated documentation as needed

## Additional context
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-->

Signed-off-by: Radoslav Dimitrov <radoslav@stacklok.com>

docs/README.md

@@ -8,6 +8,7 @@ The MCP registry provides MCP clients with a list of MCP servers, like an app st
 - **📥 Consume registry data** → [API Usage Guide](guides/consuming/use-rest-api.md)
 - **🔌 Understand the registry's purpose** → [Ecosystem vision](explanations/ecosystem-vision.md)
 - **📋 Look up specific information** → [server.json spec](reference/server-json/generic-server-json.md) | [API spec](reference/api/generic-registry-api.md) | [CLI reference](reference/cli/commands.md)
+- **🤝 Add reference to my community project** → [Community Projects](community-projects.md)
 
 ## Documentation Index