[Keyboard] Add keyboard 3dortho14u (#16329)

Co-authored-by: xia0 <xiao@morgan.net.au>

keyboards/handwired/3dortho14u/rev1/readme.md

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+# 3dortho14u
+
+![3dortho14u](https://i.imgur.com/us16LYTh.jpg)
+
+A symmetrical 14u wide ortholinear keyboard.
+
+In addition to the 3d printed parts and microcontroller, the following hardware is required:
+* 8 * 12 mm M3 bolt
+* Either:
+  * 8 * M3 muts and CA glue
+    OR
+  * 8 * 3x3 mm threaded insert
+* Optional:
+  * USB daughter board
+
+---
+
+* Keyboard Maintainer: [xia0](https://github.com/xia0)
+* Hardware Supported:
+  * Teensy 2.0 (ATmega32u4)
+* Hardware Availability: [github](https://github.com/xia0/keeb_files/tree/main/3dortho14u)
+
+Make example for this keyboard (after setting up your build environment):
+
+    make 3dortho14u/rev1:default
+
+Flashing example for this keyboard:
+
+    make 3dortho14u/rev1: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 `RESET` if it is available