Documentation update - activ layer rgb indication (#944)

* Extended documentation for the trackball LED animated light

* Docs improvement about activ layer rgb indication

docs/en/layers.md

@@ -76,26 +76,47 @@ keyboard.keymap = [
 ]
 ```
 
-## Advanced Example
+## Active Layer indication with RGB
 A common question is: "How do I change RGB background based on my active layer?"
 Here is _one_ (simple) way of many to go about it.
 
+To indicate active layer you can use RGB background, or in many cases board's status LED, then no additional hardware is needed. Information about the LED type and to which GPIO pin it is connected is often available on the pinout of the board and in the documentation.
+
+In this example on board RGB status LED is used. Number of layers is unlimited and only chosen layers can be used. Note, that LED's basic colors can have different order for different hardware.
+
 ```python
+import board
+
 from kmk.modules.layers import Layers as _Layers
 from kmk.extensions.rgb import RGB
 
-rgb = RGB(...) # your RGB configuration goes here
+sat = 255
+val = 5; # brightness in range 0-255
+
+rgb = RGB(pixel_pin=board.GP16,     # GPIO pin of the status LED, or background RGB light
+        num_pixels=1,               # one if status LED, more if background RGB light
+        rgb_order=(0, 1, 2),        # RGB order may differ depending on the hardware
+        hue_default=0,              # in range 0-255: 0/255-red, 85-green, 170-blue
+        sat_default=sat,
+        val_default=val,
+        )
+
 keyboard.extensions.append(rgb)
 
 class Layers(_Layers):
-	last_top_layer = 0
-	hues = (4, 20, 69)
-
-	def after_hid_send(self, keyboard):
-		if keyboard.active_layers[0] != self.last_top_layer:
-			self.last_top_layer = keyboard.active_layers[0]
-			rgb.set_hsv_fill(self.hues[self.last_top_layer], 255, 255)
-			rgb.hue = self.hues[self.last_top_layer]
+    last_top_layer = 0
+
+    def after_hid_send(self, keyboard):
+        if keyboard.active_layers[0] != self.last_top_layer:
+            self.last_top_layer = keyboard.active_layers[0]
+            if self.last_top_layer == 0:  # default
+                rgb.set_hsv_fill(0, sat, val)   # red
+            elif self.last_top_layer == 1:
+                rgb.set_hsv_fill(170, sat, val) # blue
+            elif self.last_top_layer == 2:
+                rgb.set_hsv_fill(43, sat, val)  # yellow
+            elif self.last_top_layer == 4:
+                rgb.set_hsv_fill(0, 0, val)     # white
 
 keyboard.modules.append(Layers())
 ```