[Keyboard] add 3w6 (#13746)

keyboards/3w6/rev2/readme.md

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+# 3W6
+
+![3W6_rev2](https://raw.githubusercontent.com/weteor/3W6/main/images/3w6_rev2_2s.jpg)
+![3W6_rev2](https://raw.githubusercontent.com/weteor/3W6/main/images/3w6_rev2_1s.jpg)
+
+The 3w6 is a low profile, split ortholinear keyboard with 36 keys.
+
+* Rev2: 
+  - onboard microcontroller (ATMega32U4)
+  - USB-C connector Board <-> PC
+  - USB-C connectors between both split halfs
+  - choc spacing (18x17mm)
+  - aggressive pinky stagger
+  - support for Choc V1 switches
+  - files for midplate (1.6 to 2mm)
+  - support for [Pimoroni Trackball](https://shop.pimoroni.com/products/trackball-breakout) instead of outer thumb switch on right half, needs midplate
+  - mounting holes for [Tenting Puck](https://splitkb.com/collections/keyboard-parts/products/tenting-puck), only usable without mid or switchplate
+
+---
+
+* Keyboard Maintainer: [weteor](https://github.com/weteor)
+* Hardware Supported: 
+    * 3w6 rev2 (with Pimoroni support)
+* Hardware Availability: 
+    * make one yourself: [Design and Productionfiles](https://github.com/weteor/3w6)
+    * maintainer is selling kits when available
+
+---
+To reach the bootloader, connect the board to the PC and push the reset button on left half.
+
+Make examples for this keyboard (after setting up your build environment):
+           
+    make 3w6/rev2:default
+    make 3w6/rev2:default_pimoroni
+   
+ ---
+
+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).