[Keyboard] Add Kay60 PCB (#15566)

Co-authored-by: Ryan <fauxpark@gmail.com>

keyboards/mechlovin/kay60/readme.md

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+# kay60
+
+![kay60](https://i.imgur.com/FVg59LUl.png)
+
+Kay60 PCB, 60% keyboard PCB.
+* Keyboard Maintainer: [Mechlovin'](https://mechlovin.studio)
+* Hardware Supported: Kay60, Atmega32U4
+* Hardware Availability: [Mechlovin'](https://mechlovin.studio)
+
+Make example for this keyboard (after setting up your build environment):
+
+    make mechlovin/kay60:default
+
+Flashing example for this keyboard:
+
+    make mechlovin/kay60:default:flash
+
+See the [build environment setup](https://docs.qmk.fm/#/getting_started_build_tools) and the [make instructions](https://docs.qmk.fm/#/getting_started_make_guide) for more information. Brand new to QMK? Start with our [Complete Newbs Guide](https://docs.qmk.fm/#/newbs).
+
+## Bootloader
+
+Enter the bootloader in 3 ways:
+
+* **Bootmagic reset**: Hold down the key at (0,0) in the matrix (usually the top left key or Escape) and plug in the keyboard
+* **Keycode in layout**: Press the key mapped to `RESET` if it is available
+* **Physic button**: Press reset swith on the bottom of the PCB