Enhance Dev's guide in docs

[sebastian-peter]

• Short intro: Creating PRs, work flow

• Requirements for approvable PRs

  • Jenkins and sonarqube runs succeed
  • Adapted readthedocs documentation to the changes
  • Wrote/adapted all relevant ScalaDoc
  • Sufficient test coverage on new/changed code
  • Optimized imports in all changed classes

• What do good tests look like?

• Code style requirements/recommendations

  • Avoid methods with side effects