Add layer condition example to encoder callback function (#15490)

Co-authored-by: filterpaper <filterpaper@localhost>

docs/feature_encoders.md

@@ -87,6 +87,43 @@ bool encoder_update_user(uint8_t index, bool clockwise) {
 
 !> If you return `true`, this will allow the keyboard level code to run, as well.  Returning `false` will override the keyboard level code.  Depending on how the keyboard level function is set up. 
 
+Layer conditions can also be used with the callback function like the following:
+
+```c
+bool encoder_update_user(uint8_t index, bool clockwise) {
+    if (get_highest_layer(layer_state|default_layer_state) > 0) {
+        if (index == 0) {
+            if (clockwise) {
+                tap_code(KC_WH_D);
+            } else {
+                tap_code(KC_WH_U);
+            }
+        } else if (index == 1) {
+            if (clockwise) {
+                tap_code(KC_VOLU);
+            } else {
+                tap_code(KC_VOLD);
+            }
+        }
+    } else {  /* Layer 0 */
+        if (index == 0) {
+            if (clockwise) {
+                tap_code(KC_PGDN);
+            } else {
+                tap_code(KC_PGUP);
+            }
+        } else if (index == 1) {
+            if (clockwise) {
+                tap_code(KC_DOWN);
+            } else {
+                tap_code(KC_UP);
+            }
+        }
+    }
+    return false;
+}
+```
+
 ## Hardware
 
 The A an B lines of the encoders should be wired directly to the MCU, and the C/common lines should be wired to ground.