Include codegen crate name in generated file header
diff --git a/codegen/src/file.rs b/codegen/src/file.rs
index 32bf047..8029afe 100644
--- a/codegen/src/file.rs
+++ b/codegen/src/file.rs
@@ -6,10 +6,9 @@
 
 pub fn write<P: AsRef<Path>>(path: P, content: TokenStream) -> Result<()> {
     let mut formatted = Vec::new();
-    write!(
-        formatted,
-        "// THIS FILE IS AUTOMATICALLY GENERATED; DO NOT EDIT\n\n"
-    )?;
+    writeln!(formatted, "// This file is @generated by syn-internal-codegen.")?;
+    writeln!(formatted, "// It is not intended for manual editing.")?;
+    writeln!(formatted)?;
 
     let mut config = rustfmt::Config::default();
     config.set().emit_mode(rustfmt::EmitMode::Stdout);