Fix typos in hello-world.rust.en-us.md

[mb720]

Hi and thanks for wasm-by-example!

I'd like to offer a few improvements to the language of hello-world.rust.en-us.md.

[netlify[bot]]

✅ Deploy Preview for wasmbyexample ready!

Name	Link
🔨 Latest commit	a634bfcc55624689e4b79eb1c11d7ae1e8bfc54f
🔍 Latest deploy log	https://app.netlify.com/sites/wasmbyexample/deploys/63c45da0484139000860f9c5
😎 Deploy Preview	https://deploy-preview-154--wasmbyexample.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site settings.