[Cask] Add a caveat to the Ardour cask

Casks/ardour.rb

@@ -15,6 +15,8 @@ cask "ardour" do
     regex(/^v?(\d+(?:\.\d+)+)$/i)
   end
   app "Ardour7.app"
+  caveats "You can find the source code here: https://github.com/Ardour/ardour
+You should consider supporting the development team, learn how to do it here: https://community.ardour.org/community"
 
   zap trash: []
 end