Add auto-generated to EmbeddedResource.cs

This update should improve the behavior of this file when referenced as source in `ThisAssembly.Resources`, such that it does not fail any analyzer or style changes.

src/EmbeddedResource.cs

@@ -1,4 +1,13 @@
-using System;
+//------------------------------------------------------------------------------
+// <auto-generated>
+//     This code was generated by a tool.
+//
+//     Changes to this file may cause incorrect behavior and will be lost if
+//     the code is regenerated.
+// </auto-generated>
+//------------------------------------------------------------------------------
+
+using System;
 using System.IO;
 using System.Linq;
 using System.Reflection;
@@ -44,4 +53,4 @@ public static Stream GetStream(string relativePath)
             Assembly.GetExecutingAssembly().GetManifestResourceStream(manifestResourceName) ??
             throw new InvalidOperationException($"Did not find required resource '{manifestResourceName}' in assembly '{baseName}'.");
     }
-}
+}