Add keyboards/converter/thinkpad_t6x/rpi_pico

[strobo5]

Description

The PCB project is linked in the info.json; it is a home-made converter PCB for Thinkpad keyboards from a wide range of models (T60, T61, X220, ...). Only two were made by me so far, so it should be seen as a one-off prototype.

Since there can be other converter PCBs for the same type of Thinkpad keyboard, I placed mine into a subfolder called rpi_pico - this might have to be more specific?

Also, thinkpad_t6x does not imply the full range of Thinkpad models from which the keyboard can be used. I don't know which are compatible (R series? T400 series up to ???). The T61 is what it is tested with.

I can load the info.json into the QMK Configurator (Ctrl+Shift+I) and it looks alright.

I'll be happy to polish this and apply feedback if this is generally considered for merging.

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).

[strobo5]

I applied qmk format-json now.

The PR guide recommends photos - I only have these at the moment to give an idea

[strobo5]

I started putting labels into the layout entries, especially for the non-obvious keys like ThinkVantage and volume control. I would continue with the rest once I find the time.