chore: add license badges (validatorjs#1732)

Co-authored-by: Rubin Bhandari <[email protected]>

README.md

@@ -5,6 +5,7 @@
 [![Downloads][downloads-image]][npm-url]
 [![Backers on Open Collective](https://opencollective.com/validatorjs/backers/badge.svg)](#backers)
 [![Sponsors on Open Collective](https://opencollective.com/validatorjs/sponsors/badge.svg)](#sponsors)
+[![License](https://img.shields.io/badge/License-MIT-red.svg)](https://github.com/alguerocode/validator.js/blob/master/LICENSE)
 [![Gitter][gitter-image]][gitter-url]
 [![Disclose a vulnerability][huntr-image]][huntr-url]