[Keyboard] Add dymium65 (#20257)

Co-authored-by: Less/Rikki <86894501+lesshonor@users.noreply.github.com>
Co-authored-by: Wycer <wycers@gmail.com>
Co-authored-by: Drashna Jaelre <drashna@live.com>
Co-authored-by: linyer-qwq <990842844@qq.com>
Co-authored-by: Linyer-qwq <32816392+Linyer-qwq@users.noreply.github.com>

keyboards/dotmod/dymium65/readme.md

@@ -0,0 +1,27 @@
+# dymium65
+
+A customizable 65% encoder keyboard.
+
+![dymium65](https://i.imgur.com/5qAl7hgh.png)
+
+* Keyboard Maintainer: [LiWenLiu](https://github.com/LiuLiuQMK)
+* Hardware Supported: dymium65 PCB with atmega32u4 microcontroller
+* Hardware Availability: Coming soon
+
+Make example for this keyboard (after setting up your build environment):
+
+    make dotmod/dymium65:default
+
+Flashing example for this keyboard:
+
+    make dotmod/dymium65: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 top left key and plug in the keyboard
+* **Physical reset button**: Briefly press the button on the back of the PCB
+* **Keycode in layout**: There is no key mapped to `QK_BOOT` in the pre-created keymaps, but you may assign this key in any keymaps you create.