⚠ Update the modules repository documentation

[Anonymxtrix]

With all the recent breaking changes to the modules repository, a detailed documentation of how to properly use it is needed. This is especially so for module development teams who are going to start to move their modules into our system.

• Add more detailed instructions to serve modules locally for cadet-frontend to consume.
• Add detailed instructions on how to create a new module using the template loader.
• Create a documented section on the extent/limitations of the current module system.