Update soft-off.md

Adding Split Peripheral Off On Press

docs/docs/behaviors/soft-off.md

@@ -38,3 +38,20 @@ By default, the keyboard will be turned off as soon as the key bound to the beha
     };
 };
 ```
+
+#### Split Peripheral Off On Press
+
+By default on split keyboards, `split-peripheral-off-on-press` is enabled. This means that while you hold down the key in the central (usually the left one), the peripheral (usually the right one) will be immediately off.
+If you want to disable this functionality, you can create a behavior, for example:
+
+```
+/ {
+    behaviors {
+        soff: soft_off {
+            compatible = "zmk,behavior-soft-off";
+            #binding-cells = <0>;s           
+            hold-time-ms = <5000>; // Only turn off if the key is held for 5 seconds or longer.
+        };
+    };
+}
+```