add "Pro Micro 87 keys"

[KD-MM2]

Description

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).

[myst729]

Just wondering why this is named after "Pro micro" 😆

[JiaGengChang]

Seems to be named pro micro because it involves soldering wires directly to the mcu (see the image in the readme here: https://i.imgur.com/SvZ9rGQ.jpeg). I could be wrong.

[drashna]

Yeah, I'm really not comfortable about the name here. ProMicro is a name that technically belongs to SparkFun. And as this isn't a board that is released by them, having it as part of the name is at best sketchy.