[Keyboard] Add Handwired 87 keys (#17682)

Co-authored-by: Drashna Jaelre <drashna@live.com>
Co-authored-by: Joel Challis <git@zvecr.com>

keyboards/handwired/hwpm87/readme.md

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+# Handwired 87 keys
+
+![hwpm87](https://i.imgur.com/DLqdtAWh.jpeg)
+
+Repaired from 87 keys keyboard using a Pro Micro
+
+* Keyboard Maintainer: [KD-MM2](https://github.com/KD-MM2)
+* Hardware Supported: Pro Micro(need to solder more pins) or any board with ATMega32u4
+* Hardware Availability: N/A (private board, might open source)
+
+First, if you have Pro Micro
+    Checkout these image for more: ![Pin map](https://i.imgur.com/SvZ9rGQ.jpeg)     ![Usabled Pins](https://i.imgur.com/Nr4cWP5.jpeg)
+    Keymaps/Handwiring: ![Handwiring](https://i.imgur.com/G1izHd6.png)
+If you have 25 GPIOs board, there is nothing to do.
+
+Second, if you are using a Capslock LED, define LED pin in: [config.h#34](https://github.com/KD-MM2/qmk_firmware/blob/hwpm87/keyboards/hwpm87/config.h#L34),
+and check the LED_PIN_ON_STATE if you get reversed led state: [config.h#35](https://github.com/KD-MM2/qmk_firmware/blob/hwpm87/keyboards/hwpm87/config.h#L35)
+
+Make example for this keyboard (after setting up your build environment):
+
+    make handwired/hwpm87:default
+
+Flashing example for this keyboard:
+
+    make handwired/hwpm87: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**: Plug cable, open QMK Toolbox and short RST pin and GND pin, then you will see it in flashmode
+* **Keycode in layout**: Press the key mapped to `RESET` if it is available