docs: Fix badge

Author: joachimvh

README.md

@@ -1,6 +1,6 @@
 # Solid Policy Engine
 
-![NPM Version](https://img.shields.io/npm/v/%40solidlab%2Fpolicy-engine)
+[![npm version](https://img.shields.io/npm/v/%40solidlab%2Fpolicy-engine](https://www.npmjs.com/package/@solidlab/policy-engine)
 
 This package provides support for both [Web Access Control](https://solidproject.org/TR/2021/wac-20210711)(WAC)
 and [Access Control Policies](https://solid.github.io/authorization-panel/acp-specification/)(ACP) authorization.