fix(docs): Add `#include` to Underglow upgrade notes

docs/blog/2022-04-02-zephyr-3-0.md

@@ -74,7 +74,7 @@ The following changes have [already been completed](https://github.com/zmkfirmwa
 
 ### RGB Underglow
 
-Zephyr's WS2812 `led_strip` driver added a new required property. When adding [underglow](/docs/features/underglow#adding-rgb-underglow-to-a-board) to a board, you now must also add a `color-mapping` property, like:
+Zephyr's WS2812 `led_strip` driver added a new required property. When adding [underglow](/docs/features/underglow#adding-rgb-underglow-to-a-board) to a board, you now must also add the additional include `#include <dt-bindings/led/led.h>` at the top of your devicetree file, and add a `color-mapping` property like:
 
 ```
 led_strip: ws2812@0 {