Add a warning to the Cargo.toml to discourage modifications

Author: shepmaster

top-crates/src/main.rs

@@ -111,5 +111,14 @@ fn main() {
 
 fn write_manifest(manifest: TomlManifest, path: impl AsRef<Path>) {
     let content = toml::to_string(&manifest).expect("Couldn't serialize TOML");
+
+    let disclaimer = "# This file is automatically @generated by the top-crates script.
+# Do not edit it manually. Any pull requests changing this file will likely be closed.
+# See https://github.com/rust-lang/rust-playground/blob/main/CRATE_POLICY.md for details.
+#
+";
+
+    let content = disclaimer.to_string() + &content;
+
     fs::write(path, content).expect("Couldn't write Cargo.toml");
 }