Add an AppStream metainfo.xml file

AppStream metainfo.xml files are like extended .desktop files used to populate app stores with information about GUI applications.  Debian and Ubunto and other major Linux distributions are starting to push for their inclusions.  This is a fairly minimal example that just covers the required entries.  The text for the description is a slightly modified version of text taken from Electrum's FAQ.

Metainfo files can contain links to screenshots.  I have not included any here, but that might be something someone would like to add in the future.

org.electrum.electrum.metainfo.xml

@@ -0,0 +1,22 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!-- Copyright 2013 Soren Stoutner <soren@stoutner.com> -->
+<component type="desktop-application">
+  <id>org.electrum.electrum</id>
+
+  <name>Electrum</name>
+  <summary>Bitcoin Wallet</summary>
+
+  <metadata_license>MIT</metadata_license>
+  <project_license>MIT</project_license>
+
+  <description>
+    <p>
+      Electrum is a lightweight Bitcoin wallet focused is speed, with low resource usage and simplifying Bitcoin.
+      Startup times are instant because it operates in conjunction with high-performance servers that handle the most complicated parts of the Bitcoin system.
+    </p>
+  </description>
+
+  <launchable type="desktop-id">electrum.desktop</launchable>
+
+  <content_rating type="oars-1.1" />
+</component>