Add comment to clarify process.exit(0) (#161)

Copied from actions/cache#1217

Author: eifinger

dist/save-cache/index.js

@@ -20,6 +20,11 @@ export async function run(): Promise<void> {
     const err = error as Error;
     core.setFailed(err.message);
   }
+  // node will stay alive if any promises are not resolved,
+  // which is a possibility if HTTP requests are dangling
+  // due to retries or timeouts. We know that if we got here
+  // that all promises that we care about have successfully
+  // resolved, so simply exit with success.
   process.exit(0);
 }