Delete Developers guide in Readme of the packages

[younesStrittmatter]

In the Readme.md files of most packages, there is still the developer's guide from the template. For example, here: autora-theorist-bsr. It doesn't make much sense to keep this in there (if at all, we should make a contribution guide so that people can contribute to these packages).

[musslick]

I agree that we should remove the developer's guide from the template!

Also: Moving this to "Ideas" since it's more of a suggestion than a question.