[Keyboard] Add kt3700 (#19432)

Co-authored-by: Sergey Vlasov <sigprof@gmail.com>
Co-authored-by: Joel Challis <git@zvecr.com>
Co-authored-by: Ryan <fauxpark@gmail.com>

keyboards/keyten/kt3700/readme.md

@@ -0,0 +1,27 @@
+# keyten kt3700
+
+Replacement pcb for Cherry G80-3700.
+
+![kt3700 image](https://i.imgur.com/s5NhDAbl.png)
+
+* Keyboard Maintainer: [keyten](https://github.com/key10iq)
+* Hardware Supported: keyten kt3700
+* Hardware Availability: [GB](https://t.me/keytenspcb/44)
+
+Make example for this keyboard (after setting up your build environment):
+
+    make keyten/kt3700:default
+	
+Flashing example for this keyboard:
+
+    make keyten/kt3700: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
+* Keycode in layout: Press the key mapped to RESET if it is available
+* Physical reset button: Hold down the BOOT0 button on the back of the PCB for a couple of seconds, then hold down the RESET button for a second