add explanation comment

Author: Hweinstock

.eslintrc.js

@@ -158,6 +158,7 @@ module.exports = {
         'unicorn/prefer-reflect-apply': 'error',
         'unicorn/prefer-string-trim-start-end': 'error',
         'unicorn/prefer-type-error': 'error',
+        // Discourage `.forEach` because it can lead to accidental, incorrect use of async callbacks.
         'unicorn/no-array-for-each': 'error',
         'security-node/detect-child-process': 'error',