Added handwired keyboard "derb_planck"

[der-b]

Description

Add new handwired keyboard "derb_planck".

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout/userspace (addition or update)
• Documentation

Issues Fixed or Closed by This PR

Checklist

• My code follows the code style of this project: C, Python
• I have read the PR Checklist document and have made the appropriate changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).

[der-b]

I adapted the code as suggested with one exception. See my commend above.

[der-b]

Thanks for the clarification. I hope, that all issues are resolved.

PS: Sorry using rules.mk and config.h instead of the info.json. I used the official documentation and this tells on to use rules.mk and config.h