[Keyboard] Add XR63GL keyboard (#19380)

keyboards/gl516/xr63gl/readme.md

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+# gl516/xr63gl
+
+![gl516/xr63gl](https://i.imgur.com/zSbrTmIh.jpg)
+
+Layout with only the Arrow key added to the 60% keyboard.
+
+* Keyboard Maintainer: [gachiham](https://github.com/gachiham)
+* Hardware Supported: XR63GL PCB, XIAO RP2040
+* Hardware Availability: [PCB Data](https://github.com/gachiham/XR63GL)
+
+Make example for this keyboard (after setting up your build environment):
+
+    make gl516/xr63gl:default
+
+Flashing example for this keyboard:
+
+    make gl516/xr63gl: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 (0,1) in the matrix (usually the top left key or Escape) and plug in the keyboard
+* **Physical reset button**: Briefly press the button on the back of the PCB - some may have pads you must short instead
+* **Keycode in layout**: Press the key mapped to `QK_BOOT` if it is available