[Keyboard] add deng/thirty keyboard (#19228)

Co-authored-by: jack <0x6a73@protonmail.com>
Co-authored-by: Drashna Jaelre <drashna@live.com>
Co-authored-by: Leo DENG <leo.deng@nio.com>

keyboards/deng/thirty/readme.md

@@ -0,0 +1,26 @@
+# Thirty
+
+![Thirty](https://i.imgur.com/4g2fcYOh.jpeg)
+
+A 3x10 toy with plenty of RGB effects.
+
+* Keyboard Maintainer: [Leo Deng](https://github.com/myst729)
+* Hardware Supported: APM32F103C8T6 (also hardware compatible with APM32F072CxT6).
+* Hardware Availability: Private Groupbuy
+
+Make example for this keyboard (after setting up your build environment):
+
+    make deng/thirty:default
+
+Flashing example for this keyboard:
+
+    make deng/thirty: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 2 ways:
+
+* **Bootmagic reset**: Hold down the top left key and plug in the keyboard
+* **Keycode in layout**: Press the key mapped to `QK_BOOT` if it is available