extend appdata.xml, add screenshot

data/com.github.ronnydo.colorpicker.appdata.xml

@@ -1,22 +1,32 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<!-- Copyright 2017 Ronny Dobra <ronnydobra at arcor dot de> -->
-<component type="desktop">
-  <id>com.github.ronnydo.colorpicker.desktop</id>
-  <metadata_license>CC0-1.0</metadata_license>
-  <project_license>GPL-3.0+</project_license>
-  <name>Color Picker</name>
-  <summary>The one and only Color Picker to speed up professionals workflow.</summary>
-  <description>
-    <p>An easy to use color picker without fancy switches and dialogs.</p>
-     <p>Features include:</p>
-     <ul>
-       <li>Color code output in multiple formats</li>
-       <li>Magnifying glass</li>
-       <li>Color history</li>
-    </ul>
-  </description>
-  <custom>
-     <value key="x-appcenter-color-primary">#603461</value>
-     <value key="x-appcenter-color-primary-text">rgb(255, 255, 255)</value>
-  </custom>
-</component>
+<?xml version="1.0" encoding="UTF-8"?>
+<!-- Copyright 2017 Ronny Dobra <ronnydobra at arcor dot de> -->
+<component type="desktop">
+  <id>com.github.ronnydo.colorpicker.desktop</id>
+  <metadata_license>CC0-1.0</metadata_license>
+  <project_license>GPL-3.0+</project_license>
+  <name>Color Picker</name>
+  <summary>The most intuitive Color Picker to speed up your workflow.</summary>
+  <description>
+    <p>One Color Picker to rule them all! No overhelming menus and settings. Just a dialog with all the features you'll need:</p>
+     <ul>
+       <li>Pick colors with the <b>Magnifying Glass</b></li>
+       <li>Choose between multiple <b>Color Formats</b></li>
+       <li>Let the <b>Color History</b> remember your last colors</li>
+    </ul>
+  </description>
+  <provides>
+	<binary>com.github.ronnydo.colorpicker</binary>
+  </provides>
+  <screenshots>
+	<screenshot type="default">
+	  <image>https://raw.githubusercontent.com/ronnydo/colorpicker/master/data/screenshot.png</image>
+	</screenshot>
+  </screenshots>
+  <developer_name>Ronny Dobra</developer_name>
+  <url type="homepage">https://github.com/RonnyDo/ColorPicker</url>
+  <url type="bugtracker">https://github.com/RonnyDo/ColorPicker/issues</url>
+  <custom>
+     <value key="x-appcenter-color-primary">#603461</value>
+     <value key="x-appcenter-color-primary-text">rgb(255, 255, 255)</value>
+  </custom>
+</component>