doc: Add fast-check to list of users

I just switched fast-check from codesandbox to pkg.pr.new to have previews of my packages for each PR. So far it works really well!

More about fast-check at https://fast-check.dev/.

README.md

@@ -77,6 +77,7 @@ These are some of the projects and companies using pkg.pr.new:
    <a href="https://wxt.dev/"><img src="https://raw.githubusercontent.com/wxt-dev/wxt/HEAD/docs/public/hero-logo.svg" alt="WXT Framework Logo" height="40" /></a>
    <a href="https://rspack.dev/"><img src="https://assets.rspack.dev/rspack/rspack-logo.svg" height="40"></a>
    <a href="https://kermanx.github.io/reactive-vscode/"><img src="https://kermanx.github.io/reactive-vscode/logo.svg" height="40"></a>
+   <a href="https://fast-check.dev/"><img src="https://raw.githubusercontent.com/dubzzz/fast-check/252853fa2984d7f1a060d92423ffd6603735c086/website/static/img/mug.svg" height="40"></a>
 </p>
 
 Feel free to add your project or company here to join the pkg.pr.new family :)