Add Djinn. (#17382)

* Add Djinn.

* Review comments.

* Further cleanup.

keyboards/tzarc/djinn/readme.md

@@ -0,0 +1,27 @@
+# Djinn
+
+![Djinn](https://i.imgur.com/ArSjkv8.jpg)
+
+The Djinn is a 64-key split keyboard -- dual 4x7 with a 4-key thumb cluster and encoders. It also has a 5-way tactile switch under the thumb. Oh, and two displays.
+
+Keyboard Maintainer: [tzarc](https://github.com/tzarc)  
+Hardware Supported: Djinn: rev1, rev2  
+Hardware Availability: [Open-source](https://github.com/tzarc/djinn)
+
+Make example for this keyboard (after setting up your build environment):
+
+    make tzarc/djinn/rev2:default
+
+Flashing example for this keyboard:
+
+    make tzarc/djinn/rev2: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-left key 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 `QK_BOOT` if it is available.