Add a layer opacity example

examples/layer-opacity.html

@@ -0,0 +1,17 @@
+---
+layout: example.html
+title: Layer Opacity
+shortdesc: Adjust layer opacity based on user input
+docs: >
+  The `layer.setOpacity()` method can be called to adjust the opacity of a layer.
+tags: "opacity"
+cloak:
+  - key: get_your_own_D6rA4zTHduk6KOKTXzGB
+    value: Get your own API key at https://www.maptiler.com/cloud/
+---
+<div id="map" class="map"></div>
+<label>
+  Layer opacity
+  <input id="opacity-input" type="range" min="0" max="1" step="0.01" value="1" />
+  <span id="opacity-output"></span>
+</label>