Update led_update_kb example (#7451)

* Update led_update_kb example

* Update comment to explain pin behavior

* wordsmith

* wordsmithing 2

docs/custom_quantum_functions.md

@@ -132,31 +132,16 @@ Some examples include:
 bool led_update_kb(led_t led_state) {
     bool res = led_update_user(led_state);
     if(res) {
-        if (led_state.num_lock) {
-            writePinLow(B0);
-        } else {
-            writePinHigh(B0);
-        }
-        if (led_state.caps_lock) {
-            writePinLow(B1);
-        } else {
-            writePinHigh(B1);
-        }
-        if (led_state.scroll_lock) {
-            writePinLow(B2);
-        } else {
-            writePinHigh(B2);
-        }
-        if (led_state.compose) {
-            writePinLow(B3);
-        } else {
-            writePinHigh(B3);
-        }
-        if (led_state.kana) {
-            writePinLow(B4);
-        } else {
-            writePinHigh(B4);
-        }
+        // writePin sets the pin high for 1 and low for 0.
+        // In this example the pins are inverted, setting
+        // it low/0 turns it on, and high/1 turns the LED off.
+        // This behavior depends on whether the LED is between the pin
+        // and VCC or the pin and GND.
+        writePin(B0, !led_state.num_lock);
+        writePin(B1, !led_state.caps_lock);
+        writePin(B2, !led_state.scroll_lock);
+        writePin(B3, !led_state.compose);
+        writePin(B4, !led_state.kana);
     }
     return res;
 }