docs: mention eslint flat config

Author: haoqunjiang

README.md

@@ -11,7 +11,7 @@ other parts of `@vue/cli`/`create-vue` setups.
 
 ## Installation
 
-In order to work around [a known limitation in ESLint](https://github.com/eslint/eslint/issues/3458), we recommend you to use this package alongside `@rushstack/eslint-patch`, so that you don't have to install too many dependencies:
+Before [ESLint Flat Config](https://eslint.org/docs/latest/use/configure/configuration-files-new) becomes stable, in order to work around [a known limitation in ESLint](https://github.com/eslint/eslint/issues/3458), we recommend you to use this package alongside `@rushstack/eslint-patch`, so that you don't have to install too many dependencies:
 
 ```sh
 npm add --dev @vue/eslint-config-prettier @rushstack/eslint-patch