Disable ZMK Studio, add full README, fix LED chain-length

Studio commented out in config with re-enable instructions in README.
LED chain-length corrected to 27 (6 underglow + 21 per-key per half).

boards/shields/corne/boards/nice_nano.overlay

@@ -31,7 +31,7 @@
         spi-max-frequency = <4000000>;
 
         /* WS2812 */
-        chain-length = <10>; /* arbitrary; change at will */
+        chain-length = <27>; /* 6 underglow + 21 per-key per half */
         spi-one-frame = <0x70>;
         spi-zero-frame = <0x40>;
 

boards/shields/corne/boards/nice_nano_v2.overlay

@@ -31,7 +31,7 @@
         spi-max-frequency = <4000000>;
 
         /* WS2812 */
-        chain-length = <10>; /* arbitrary; change at will */
+        chain-length = <27>; /* 6 underglow + 21 per-key per half */
         spi-one-frame = <0x70>;
         spi-zero-frame = <0x40>;
 

boards/shields/corne/corne.zmk.yml

@@ -9,7 +9,7 @@ features:
   - keys
   - display
   - underglow
-  - studio
+
 siblings:
   - corne_left
   - corne_right