docs(README): add link to npm downloads badge (#10467)

Author: Olexandr88

README.md

@@ -5,7 +5,7 @@
 [![npm audit](https://jenkins.swagger.io/buildStatus/icon?job=oss-swagger-ui-security-audit&subject=npm%20audit)](https://jenkins.swagger.io/job/oss-swagger-ui-security-audit/lastBuild/console)
 [![total GitHub contributors](https://img.shields.io/github/contributors-anon/swagger-api/swagger-ui.svg)](https://github.com/swagger-api/swagger-ui/graphs/contributors)
 
-![monthly npm installs](https://img.shields.io/npm/dm/swagger-ui.svg?label=npm%20downloads)
+[![monthly npm installs](https://img.shields.io/npm/dm/swagger-ui.svg?label=npm%20downloads)](https://www.npmjs.com/package/swagger-ui)
 ![docker registry](https://img.shields.io/badge/docker-docker.swagger.io%2Fswaggerapi%2Fswagger--ui-blue)
 ![monthly packagist installs](https://img.shields.io/packagist/dm/swagger-api/swagger-ui.svg?label=packagist%20installs)
 ![gzip size](https://img.shields.io/bundlephobia/minzip/swagger-ui.svg?label=gzip%20size)