Add base Ryujin firmware (#17187)

Co-authored-by: Drashna Jaelre <drashna@live.com>
Co-authored-by: Wolf Van Herreweghe <wolfvh@getupgamesofficial.com>

keyboards/wolf/ryujin/readme.md

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+# Ryujin
+
+The following is the QMK Firmware for the Ryujin PCB.
+
+The PCB features:
+* QMK & VIA compatibility
+
+---
+
+* Keyboard Maintainer: [ToastyStoemp](https://github.com/ToastyStoemp)
+
+Make example for this keyboard (after setting up your build environment):
+
+    make wolf/ryujin:default
+
+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 ESC key and plug in the keyboard (Top Left most switch)
+* **Physical reset button**: Briefly press the button on the back of the PCB
+* **Keycode in layout**: Press the B key on layer 1 which is mapped to `RESET`