Add Tonuino Manager website and Sparkle updates

appcast.xml

@@ -0,0 +1,9 @@
+<?xml version="1.0" encoding="utf-8"?>
+<rss version="2.0" xmlns:sparkle="http://www.andymatuschak.org/xml-namespaces/sparkle" xmlns:dc="http://purl.org/dc/elements/1.1/">
+  <channel>
+    <title>Tonuino Manager Updates</title>
+    <link>https://tonuino.maddin.app/</link>
+    <description>Updates for Tonuino Manager for macOS</description>
+    <language>de</language>
+  </channel>
+</rss>