Update 20210529.md (qmk#13170)

This was confusing to me when I updated, so I want to make it more clear for those that come after.

docs/ChangeLog/20210529.md

@@ -82,6 +82,22 @@ Example code before change:
 void encoder_update_kb(uint8_t index, bool clockwise) {
     encoder_update_user(index, clockwise);
 }
+
+void encoder_update_user(uint8_t index, bool clockwise) {
+    if (index == 0) { /* First encoder */
+        if (clockwise) {
+            tap_code(KC_PGDN);
+        } else {
+            tap_code(KC_PGUP);
+        }
+    } else if (index == 1) { /* Second encoder */
+        if (clockwise) {
+            tap_code(KC_DOWN);
+        } else {
+            tap_code(KC_UP);
+        }
+    }
+}
 ```
 
 Example code after change:
@@ -90,6 +106,25 @@ Example code after change:
 bool encoder_update_kb(uint8_t index, bool clockwise) {
     return encoder_update_user(index, clockwise);
 }
+
+bool encoder_update_user(uint8_t index, bool clockwise) {
+    if (index == 0) { /* First encoder */
+        if (clockwise) {
+            tap_code(KC_PGDN);
+        } else {
+            tap_code(KC_PGUP);
+        }
+    } else if (index == 1) { /* Second encoder */
+        if (clockwise) {
+            tap_code(KC_DOWN);
+        } else {
+            tap_code(KC_UP);
+        }
+    }
+    return true; 
+    // 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.
+}
 ```
 
 ## Core Changes :id=core-changes