[Keyboard] Add Viendi8L (#17943)

Co-authored-by: Ryan <fauxpark@gmail.com>

keyboards/viendi8l/readme.md

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+# Viendi8L PCB firmware
+
+![8L_image](https://imgur.com/z4cuSYJh.png)
+
+The 8L 80% (60% plus southpaw numpad) keyboard designed by Viendi, with PCB by Gondolindrim.
+
+* Keyboard Maintainer: [Gondolindrim](https://github.com/gondolindrim)
+* Hardware Availability: proprietary PCB
+* Website: [Viendi](https://viendi.co/)
+
+## How to flash
+
+### Enter bootloader
+
+* **Bootmagic reset**: hold down the key at (0,0) in the matrix (the encoder push) and plug in the keyboard, waiting for five seconds
+* **Physical reset button**: press the button on the front of the PCB or use pliers to short the reset contacts, for at least five seconds
+* **Keycode in layout**: press the key mapped to `RESET` if it is available (ESC key at layer 1 in the default layout)
+
+## Compile firmware
+
+After accessing the DFU state in your PCB, build the default layout using:
+
+    make viendi8l:default
+
+Then download the resulting binary `*bin` file using `dfu-util` or QMK Toolbox.
+
+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).