Add code to get assembly reference to resource project.

osu.Game.Resources/ResourceAssembly.cs

@@ -0,0 +1,9 @@
+using System.Reflection;
+
+namespace osu.Game.Resources
+{
+    public static class ResourceAssembly
+    {
+        public static Assembly Assembly => typeof(ResourceAssembly).Assembly;
+    }
+}