Sources file description

The final user will not able to use the application, because e.g. sources.yml does not exist in the repository.

It is also nowhere said who it should look like. The sources.yml is very important, and should also be versioned. This is our primary 'database' and it will be large: think of about 40 various models, for each ca. 17 lines, i.e. ca. 700 lines...