[Keyboard] Add xdboards/recon keyboard (#24135)

Co-authored-by: Drashna Jaelre <drashna@live.com>

keyboards/xdboards/recon/readme.md

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+# xdboards/recon
+
+![xdboards/recon](https://imgur.com/a/HcjT4yq)
+
+A split low profile keyboard with hotswap sockets that is built around the Sea-Picro microcontroller for it's dedicated RGB pin.
+
+* Keyboard Maintainer: [Daniel Weeks](https://github.com/Xanimos)
+* Hardware Supported: Recon PCB, Sea-Picro, backwards compatibility with ProMicro pin layout.
+* Hardware Availability: [xdboards.xyz shop](https://www.xdboards.xyz)
+
+Make example for this keyboard (after setting up your build environment):
+
+    make xdboards/recon: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).
+
+## Bootloader
+
+Enter the bootloader in 2 ways:
+
+* **Physical reset button**: Briefly press the button on the side of the PCB
+* **Keycode in layout**: Press the key mapped to `QK_BOOT` if it is available
+* **Boot Magic**: Hold down the boot magic key while plugging in the USB cable
+
+## Setup for Sea-Picro microcontrollers
+
+To take advantage of the dedicated 5v RGB pin on the sea-picro you must create your keymap
+and then add a `rules.mk` file and copy and paste the following:
+```
+CONVERT_TO = rp2040_ce
+USE_SEA_PICRO_RGB_PIN = yes
+```
+
+If you do not want to use the dedicated 5v RGB header then follow the Setup for non Sea-Picro microcontrollers.
+
+## Setup for non Sea-Picro microcontrollers
+
+Solder the "Pro-Micro Compatibility" jumper on the bottom of both boards.
+
+In your keymap directory:
+  - add/modify a `rules.mk` file
+    - Remove or set `CONVERT_TO` to desired converter see [QMK Documentation](https://docs.qmk.fm/#/feature_converters)
+    - Remove or set `USE_SEA_PICRO_RGB_PIN` to `no`
+
+
+## Setup for Underglow rgb only
+
+
+Solder the "Per-Key RGB Skip" jumper on the bottom of both boards. Do not install per key RGBs.
+
+In your keymap directory:
+  - add/modify a `config.h` file and insert 
+    ```
+    #define RGB_MATRIX_SPLIT { 5, 5 }
+    #define RGB_MATRIX_LED_COUNT 10
+    ```
+