[Keyboard] add cypher rev6 (#14647)

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

keyboards/cablecardesigns/cypher/rev6/readme.md

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+# cypher rev6
+
+PCB for the cypher keyboard, this is rev6 of this PCB
+
+* Keyboard Maintainer: [westfoxtrot](https://github.com/westfoxtrot)
+* Hardware Supported: Cypher PCB revisions 6 (Rev # is printed on PCB)
+* Hardware Availability: with keyboard release + [Files released here](https://github.com/westfoxtrot/Cypher_PCB)
+
+Make example for this keyboard (after setting up your build environment):
+
+    make cablecardesigns/cypher/rev6:default
+
+Flashing example for this keyboard:
+
+    make cablecardesigns/cypher/rev6: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**: There are 2 holes underneath the spacebar position that if shorted will enter bootloader
+* **Keycode in layout**: Press the key mapped to `RESET` if it is available