Modernize the AppStream metadata

appveyor.yml

@@ -59,7 +59,7 @@ for:
   - sh: cp ../resources/pictures/carton.png milkytracker.png
   - sh: cp ../resources/milkytracker.desktop .
   - sh: sed -i 's|MilkyTracker|Milkytracker|g;s|Comment=.*|Comment=A Portable SampleTracker DAW|g' milkytracker.desktop
-  #- sh: cp ../resources/milkytracker.appdata /usr/share/metainfo
+  #- sh: cp ../resources/org.milkytracker.MilkyTracker.metainfo.xml /usr/share/metainfo/
   - sh: find .
   - sh: cd .. 
   - sh: wget 'https://github.com/AppImage/AppImageKit/releases/download/continuous/appimagetool-x86_64.AppImage';

resources/org.milkytracker.MilkyTracker.metainfo.xml

@@ -0,0 +1,28 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<component type="desktop-application">
+  <id>org.milkytracker.MilkyTracker</id>
+  <launchable type="desktop-id">milkytracker.desktop</launchable>
+  <metadata_license>CC0-1.0</metadata_license>
+  <project_license>GPL-3.0+ AND BSD-3-Clause</project_license>
+  <provides>
+    <binary>milkytracker</binary>
+  </provides>
+  <name>MilkyTracker</name>
+  <developer_name>The MilkyTracker team</developer_name>
+  <summary>Fast Tracker II inspired music tracker</summary>
+  <description>
+    <p>
+      MilkyTracker is an open source, multi-platform music application for creating .MOD and .XM module files.
+      It attempts to recreate the module replay and user experience of the popular DOS program Fasttracker II,
+      with special playback modes available for improved Amiga ProTracker 2/3 compatibility.
+    </p>
+  </description>
+  <screenshots>
+    <screenshot type="default">
+      <image type="source">https://milkytracker.org/screenshots/desktop/raina-Default.png</image>
+    </screenshot>
+  </screenshots>
+  <url type="homepage">https://milkytracker.org/</url>
+  <update_contact>milkytracker_at_chrisoneill.co.uk</update_contact>
+  <content_rating type="oars-1.1"/>
+</component>