[Keyboard] Add Devil68 Pro (#15820)

keyboards/horrortroll/chinese_pcb/devil68_pro/readme.md

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+# Devil68 Pro
+
+Support Atmega32u4 keyboard.
+
+* Keyboard Maintainer: [HorrorTroll](https://github.com/HorrorTroll)
+* Hardware Supported: Atmega32u4
+
+Make example for this keyboard (after setting up your build environment):
+
+    make horrortroll/chinese_pcb/devil68_pro:default
+
+Flashing example for this keyboard:
+
+    make horrortroll/chinese_pcb/devil68_pro: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 (3,6) in the matrix (B key) and plug in the keyboard
+* **Reset by wire**: Using a wire, 1 head to GND hole and other one to Reset pin on MCU
+* **Keycode in layout**: Press the key mapped to RESET if it is available