add example code about Utility Functions

docs/feature_rgblight.md

@@ -189,6 +189,14 @@ If you need to change your RGB lighting in code, for example in a macro to chang
 |`rgblight_set()`                            |Flash out led buffers to LEDs              |
 |`rgblight_set_clipping_range(pos, num)`     |Set clipping Range. see [Clipping Range](#clipping-range) |
 
+Example:
+```c
+sethsv(HSV_WHITE, (LED_TYPE *)&led[0]); // led 0
+sethsv(HSV_RED,   (LED_TYPE *)&led[1]); // led 1
+sethsv(HSV_GREEN, (LED_TYPE *)&led[2]); // led 2
+rgblight_set(); // Utility functions do not call rgblight_set() automatically, so they need to be called explicitly.
+```
+
 ### Effects and Animations Functions
 #### effect range setting
 |Function                                    |Description       |