[Keyboard] Add KMAC PAD (#13104)

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

keyboards/kmac_pad/readme.md

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+# KMAC PAD
+
+![kmac_pad](https://i.imgur.com/4P1ybgNl.jpg)
+
+KMAC PAD is a num pad keyboard.
+It can be used independently, but can also be used by connecting with KMAC keyboard case.
+
+* Keyboard Maintainer: [talsu](https://github.com/talsu)
+* Hardware Supported: KMAC PAD
+* Hardware Availability: http://www.kbdmania.net/xe/news/5232321
+
+Make example for this keyboard (after setting up your build environment):
+
+    make kmac_pad:default
+    
+Flashing example for this keyboard:
+
+    make kmac_pad: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
+
+The PCB is hardwired to run the bootloader if the key at the `FN` position (the only key in first row) is held down when connecting the keyboard.
+
+## PCB
+
+![Imgur](https://i.imgur.com/ML66cvfl.jpg)
+![Imgur](https://i.imgur.com/Kr2Wdtkl.jpg)
+
+### Switch Pins
+
+The FN key in the `Row 0` is directly connected to the E2 pin.   
+The rest of the rows below that use MATRIX. (`Row 1 ~ Row 5`)
+| Row   | Pin                    |
+|:-----:| ---------------------- |
+| 0     | x (Not in Matrix)      |
+| 1     | D0                     |
+| 2     | D1                     |
+| 3     | D2                     |
+| 4     | D3                     |
+| 5     | D5                     |
+
+| Column | Pin                   |
+|:------:| --------------------- |
+| 0      | C7                    |
+| 1      | C6                    |
+| 2      | B6                    |
+| 3      | B5                    |
+
+### Backlight Pins
+
+There are 2 pins for backlight.
+
+The LED of the FN key uses pin `B3`.
+All other keys are connected to the `B1` pin.