[Keymap] addition: macro for "screenshot region to clipboard" in macOS (#5505)

[Keymap] addition: macro for "screenshot region to clipboard" in macOS (#5505)

* Create custom Planck Light keycap

See README for details

* Link to WhatPulse in README

* More remapping, and add RGB LED effects

* Remove dead code, address PR feedback from @drashna

* Add macro for “screenshot region to clipboard” hotkey for macOS

Also remove unused layer / key logic

* Remove extraneous comment

* Incorporate PR feedback from @drashna.

Update README with new mapping.