fix(docs): Clarify backlight & underglow use cases

This should help reduce confusion for newcomers.

docs/docs/features/backlight.md

@@ -6,7 +6,11 @@ sidebar_label: Backlight
 import Tabs from '@theme/Tabs';
 import TabItem from '@theme/TabItem';
 
-Backlight is a feature used to control array of LEDs, usually placed through or under switches. Unlike [RGB Underglow](underglow.md), backlight currently allows only one color per LED, also LEDs are not addressable, so you can't control individual LEDs.
+Backlight is a feature used to control an array of LEDs, usually placed through or under switches.
+
+:::info
+Unlike [RGB Underglow](underglow.md), backlight can only control single color LEDs. Additionally, because backlight LEDs all receive the same power, it's not possible to dim individual LEDs.
+:::
 
 ## Enabling Backlight
 

docs/docs/features/underglow.md

@@ -5,6 +5,10 @@ sidebar_label: RGB Underglow
 
 RGB underglow is a feature used to control "strips" of RGB LEDs. Most of the time this is called underglow and creates a glow underneath the board using a ring of LEDs around the edge, hence the name. However, this can be extended to be used to control anything from a single LED to a long string of LEDs anywhere on the keyboard.
 
+:::info
+RGB underglow can also be used for under-key lighting. If you have RGB LEDs on your keyboard, this is what you want. For PWM/single color LEDs, see [Backlight](backlight.md).
+:::
+
 ZMK supports all the RGB LEDs supported by Zephyr. Here's the current list supported:
 
 - WS2812-ish (WS2812B, WS2813, SK6812, or compatible)