appdata: Add <releases> section

This is used by applications like GNOME Software to show release notes,
by Flatpak to determine the human-facing version number for the
application, and is now mandatory for applications on Flathub.

https://www.freedesktop.org/software/appstream/docs/chap-Metadata.html#tag-releases

others/appdata/megaglest.appdata.xml

@@ -37,6 +37,21 @@
   <url type="translate">http://translate.megaglest.org</url>
   <developer_name>The MegaGlest Team</developer_name>
   <update_contact>contact_at_megaglest.org</update_contact>
+  <releases>
+    <release version="3.13.0" date="2017-03-09">
+      <url>https://megaglest.org/news/44/17/MegaGlest-3.13.0-released</url>
+      <description>
+        <p>The MegaGlest team is proud to release v3.13.0. Notable improvements to this release include:</p>
+        <ul>
+          <li>Multi-building select and key-binding for production of units</li>
+          <li>Buildings of the same type can be added to a control group, which means multiple units can be produced with a single click</li>
+          <li>A crash (out of sync) that sometimes happened when playing with Fog-of-War disabled has been fixed</li>
+          <li>Improved AI behavior</li>
+          <li>To help keep multi-player games more balanced and to ensure that players are practiced enough to harvest resources and beat a normal CPU, a scenario is automatically launched the first time a user tries to enter the lobby. The scenario must be won before the player can actually enter the lobby.</li>
+        </ul>
+      </description>
+    </release>
+  </releases>
   <content_rating type="oars-1.0">
     <content_attribute id="violence-cartoon">none</content_attribute>
     <content_attribute id="violence-fantasy">moderate</content_attribute>