UTY-1060: Prepend warning to copied schema files (#612)

Author: paulbalaji

CHANGELOG.md

@@ -7,6 +7,7 @@
 - Added support for the Steam authentication flow.
 - Added a reference to Blank Starter Project in the README.
 - Added Frames Per Second (FPS) and Unity heap usage as metrics sent by `MetricSendSystem.cs`.
+- Added a warning message to the top of schema files copied into the `from_gdk_packages` directory.
 
 ### Changed
 

workers/unity/Packages/com.improbable.gdk.tools/GenerateCode.cs

@@ -14,7 +14,12 @@ internal static class GenerateCode
         private const string FromGdkPackagesDir = "from_gdk_packages";
         private const string ImprobableJsonDir = "build/ImprobableJson";
 
-
+        private static string SchemaWarningMessage =
+            "// ------------------------------------------------------------------------" + Environment.NewLine +
+            "// WARNING: DO NOT EDIT." + Environment.NewLine +
+            "// Any changes made to this file will be overwritten by the Code Generator." + Environment.NewLine +
+            "// ------------------------------------------------------------------------" + Environment.NewLine +
+            Environment.NewLine;
 
         private static readonly string SchemaCompilerRelativePath =
             $"../build/CoreSdk/{Common.CoreSdkVersion}/schema_compiler/schema_compiler";
@@ -206,7 +211,7 @@ private static void CopySchemaFiles(string schemaRoot, KeyValuePair<string, stri
                     }
                 }
 
-                File.Copy(file, to);
+                File.WriteAllText(to, SchemaWarningMessage + File.ReadAllText(file));
             }
         }