[Keyboard] add kbd75rgb support (#15552)

* add kbd75rgb support

* Update keyboards/kbdfans/kbd75rgb/config.h

* Update keyboards/kbdfans/kbd75rgb/rules.mk

* Update keyboards/kbdfans/kbd75rgb/rules.mk

* Update keymap.c

* Update keymap.c

* Update readme.md

* Update keyboards/kbdfans/kbd75rgb/config.h

* Update keyboards/kbdfans/kbd75rgb/config.h

* Update keyboards/kbdfans/kbd75rgb/config.h

* Update keyboards/kbdfans/kbd75rgb/rules.mk

* Update keyboards/kbdfans/kbd75rgb/rules.mk

* Update keyboards/kbdfans/kbd75rgb/keymaps/default/keymap.c

* Update keyboards/kbdfans/kbd75rgb/keymaps/default/keymap.c

* Update keyboards/kbdfans/kbd75rgb/keymaps/default/keymap.c

* Update keyboards/kbdfans/kbd75rgb/keymaps/default/keymap.c

* Update keyboards/kbdfans/kbd75rgb/rules.mk

keyboards/kbdfans/kbd75rgb/readme.md

@@ -0,0 +1,23 @@
+# KBD75RGB
+
+A customizable 75% RGB keyboard.
+
+* Keyboard Maintainer: [moyi4681](https://github.com/moyi4681)
+* Hardware Supported: KBDFANS
+* Hardware Availability: [kbdfans](https://kbdfans.myshopify.com/)
+
+
+## Bootloader
+
+Enter the bootloader in 3 ways:
+
+* **Bootmagic reset**: Hold down the key at (0,0) in the matrix
+* **Physical reset button**: Briefly press the button on the back of the PCB
+* **Keycode in layout**: Press the key mapped to `RESET` if it is available
+
+
+Make example for this keyboard (after setting up your build environment):
+
+    make kbdfans/kbd75rgb: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).