Adds support for XD84 Pro (#9750)

Co-authored-by: Ryan <fauxpark@gmail.com>
Co-authored-by: katawajojo <vibri@localhost>
Co-authored-by: katawajojo <katawajojo@vibri.local>

keyboards/xd84pro/dev.md

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+# XD84 Pro
+
+Development docs covering the following:
+- ATmega32u4
+- RGB
+- Backlight
+- Light Through Cat
+
+### Bootloader
+Default bootloader is `atmel-dfu`.
+Reboot to bootloader via bridging 2 contacts points in the icsp header.
+Flash using regular dfu methods.
+
+# RGB
+- PIN F6
+- Number of RGB LED: 12
+
+# Backlight
+- PIN F5
+
+# Light Through Cat
+- PIN F5
+
+# Caps Lock LED/Indicator
+- PIN B2
+
+## Return to stock firmware
+The original TMK firmware is available at [xd.tkg.io](https://xd.tkg.io).