docs: add OpenSSF Scorecard badge

https://github.com/expressjs/discussions/issues/162

Readme.md

@@ -5,6 +5,7 @@
   [![NPM Version][npm-version-image]][npm-url]
   [![NPM Install Size][npm-install-size-image]][npm-install-size-url]
   [![NPM Downloads][npm-downloads-image]][npm-downloads-url]
+  ![OpenSSF Scorecard Badge](https://api.securityscorecards.dev/projects/github.com/ada-url/expressjs/express)
 
 ```js
 const express = require('express')