SLING-13150 - Document MCP server usage

[rombert]

No description provided.

[rombert]

Draft until the bundles are released. In the meantime, the following command can be used for testing the MCP functionality:

docker run --rm -p 8080:8080 \
      -v "$HOME/.m2/repository:/opt/sling/m2repo:ro" \
      apache/sling:snapshot oak_tar \
      --extra-features mvn:org.apache.sling/org.apache.sling.mcp-server/0.1.5-SNAPSHOT/slingosgifeature/main mvn:org.apache.sling/org.apache.sling.mcp-server-contributions/0.1.1-SNAPSHOT/slingosgifeature/main

This requires the latest changes pushed today, so a docker pull may be needed if the Sling Starter Docker image was recently built locally.