make contributing clearer

Signed-off-by: Luke-zhang-04 <[email protected]>

Author: Luke-zhang-04

Diff for: CONTRIBUTING.md

@@ -100,7 +100,7 @@ pub fn cargo(contents: &str) -> Result<usize> {
 package_managers.insert(
     String::from("Cargo.toml"), // File name
 
-    // Parser function, then writeln! macro
+    // Parser function, then the corresponding element from the PackageManager enum
     (package_parser::cargo, package_manager::PackageManager::Cargo),
 );
 ```