Add some icons (#285)

menu-demo/background.js

@@ -52,7 +52,11 @@ browser.menus.create({
   type: "radio",
   title: browser.i18n.getMessage("menuItemGreenify"),
   contexts: ["all"],
-  checked: true
+  checked: true,
+  icons: {
+    "16": "icons/paint-green-16.png",
+    "32": "icons/paint-green-32.png"
+  }
 }, onCreated);
 
 browser.menus.create({
@@ -60,7 +64,11 @@ browser.menus.create({
   type: "radio",
   title: browser.i18n.getMessage("menuItemBluify"),
   contexts: ["all"],
-  checked: false
+  checked: false,
+  icons: {
+    "16": "icons/paint-blue-16.png",
+    "32": "icons/paint-blue-32.png"
+  }
 }, onCreated);
 
 browser.menus.create({

menu-demo/icons/LICENSE

@@ -1,2 +1,4 @@
 
 The "page-32.png" and "page-48.png" icons are taken from the miu iconset created by Linh Pham Thi Dieu, and are used under the terms of its license: http://linhpham.me/miu/.
+
+The "paint-blue-16", "paint-blue-32", "paint-green-16", and "paint-green-32" icons are adapted from an icon in the ["Outline icons" set](https://www.iconfinder.com/icons/1021026/paint_icon).