[Keyboard] Added Jels88 (#15090)

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

keyboards/jels/jels88/readme.md

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+# jels88
+
+![jels88](https://i.imgur.com/7kuYR4G.png)
+
+* Keyboard Maintainer: [jels](https://github.com/Jels-kb)
+* Hardware Supported: jels88b/jels88c PCB
+* Hardware Availabililty: Group buys, Various dates.
+
+Make example for this keyboard (after setting up your build environment):
+    
+    make jels/jels88:default
+
+Flashing example for this keyboard:
+
+    make jels/jels88: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 top right key (ESC) and plug in the keyboard
+* **Physical reset button**: Briefly press the button on the back of the PCB
+* **Keycode in layout**: Press the key mapped to `RESET` if it is available