[Keyboard] Add Kintsugi keyboard (#15439)

keyboards/adpenrose/kintsugi/readme.md

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+# Kintsugi
+
+![kintsugi](https://i.imgur.com/HPdmzdCl.jpeg)
+
+A 65%-ish keyboard with some extra features.
+
+## Features
+
+* Powered by an ATmega32u4 microcontroller (current version needs an Elite-C to work).
+* Encoder.
+* OLED screen.
+* Underglow.
+* Hotswap sockets.
+
+## General info
+
+* Keyboard Maintainer: [Arturo Avila](https://github.com/ADPenrose)
+* Hardware Supported: Kintsugi V1 PCB
+* Hardware Availability: [Arturo Avila](https://github.com/ADPenrose)
+
+Make example for this keyboard (after setting up your build environment):
+
+    make kintsugi:default
+
+Flashing example for this keyboard:
+
+    make kintsugi: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
+* **Physical reset button**: Briefly press the button on the front of the Elite-C microcontroller _**before soldering**_ it to the PCB- some may have pads you must short instead
+* **Keycode in layout**: Press the key mapped to `RESET` if it is available