[Docs] Update feature_rgblight.md (#11363)

* Update feature_rgblight.md

The note is meant to let people know that this is specific to RGB Backlight and does not work with RGB Matrix based implementations.

* Update docs/feature_rgblight.md

Co-authored-by: Drashna Jaelre <drashna@live.com>

Co-authored-by: Drashna Jaelre <drashna@live.com>

docs/feature_rgblight.md

@@ -187,6 +187,8 @@ const uint8_t RGBLED_GRADIENT_RANGES[] PROGMEM = {255, 170, 127, 85, 64};
 
 ## Lighting Layers
 
+?> **Note:** Lighting Layers is an RGB Light feature, it will not work for RGB Matrix. See [RGB Matrix Indicators](feature_rgb_matrix.md?indicators) for details on how to do so.
+
 By including `#define RGBLIGHT_LAYERS` in your `config.h` file you can enable lighting layers. These make
 it easy to use your underglow LEDs as status indicators to show which keyboard layer is currently active, or the state of caps lock, all without disrupting any animations. [Here's a video](https://youtu.be/uLGE1epbmdY) showing an example of what you can do.