[Keyboard] Add CXT Studio (#19531)

Co-authored-by: jack <0x6a73@protonmail.com>
Co-authored-by: Joel Challis <git@zvecr.com>
Co-authored-by: Drashna Jaelre <drashna@live.com>
Co-authored-by: Ryan <fauxpark@gmail.com>
Co-authored-by: Colin Kinloch <colin.kinloch@collabora.com>

keyboards/cxt_studio/readme.md

@@ -0,0 +1,27 @@
+# cxt_studio
+
+![cxt_studio](https://i.imgur.com/AMCTioSh.jpeg)
+
+3x4 ortho rgb lighting 4 knobs.
+
+* Keyboard Maintainer: [Colin Kinloch](https://github.com/ColinKinloch)
+* Hardware Supported: CXT-Studio
+* Hardware Availability: AliExpress. I think the manufacturer is on Taobao.
+
+Make example for this keyboard (after setting up your build environment):
+
+    make cxt_studio:default
+
+Flashing example for this keyboard:
+
+    make cxt_studio: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 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