Explain how to add a new repository to the workspace

Things to watch out:

- In case it uses other private projects from the workspace, it should add the MALIPUT_TOKEN
- In case it requires CI, we should try to copy the workflows we already have to provide support for gcc, clang, and scan-build
- Naming conventions
- etc

Review the existing workspace repository documentation and CI workflows first, especially the examples supporting gcc, clang, and scan-build. Document the steps for adding a repository, including private-project access with MALIPUT_TOKEN, CI coverage, and naming conventions; the documentation should also explain any remaining workspace-specific considerations.

Written by the indexing model from the issue text.