C#: Add auto generated comment to generated models as data files.

misc/scripts/models-as-data/generate_flow_model.py

@@ -133,6 +133,9 @@ Requirements: `codeql` should both appear on your path.
 
     def asCsvModel(self, superclass, kind, rows):
         classTemplate = """
+/**
+ * THIS FILE IS AN AUTO-GENERATED MODELS AS DATA FILE. DO NOT EDIT.
+ */
 private class {0}{1}Csv extends {2} {{
     override predicate row(string row) {{
         row =