Updated personal keymaps, fixed Let's Split default keymap, updated JJ40 README ...

Updated personal keymaps, fixed Let's Split default keymap, updated JJ40 README (#2704)

* Add M6-A keymap

* Update XD60 keymap

* Update XD60 keymap readme

* Update JJ40 and Let's Split keymaps

* Add readme for M6-A

* Fix typo, update JJ40 README

* Update jj40 readme

* Cleanup jj40 keymap

* Revert Let's Split QWERTY layer to default before #2010

* Update numpad layers

* Fix: Let's Split keymap getting stuck mods due to having keycodes assigned on the Raise layer

* Keep ASCII art consistent with keymap