[Rust] Add Rustlings chapter 3 and 4

[henchiyb]

Description

• Add the blog post for Rustlings chapter 3 and 4

Related Issue

https://github.com/lowlevelers/lowlevelers.com/issues/12

[netlify[bot]]

✅ Deploy Preview for dynamic-faloodeh-e195d3 ready!

Name	Link
🔨 Latest commit	c00318e933c4314b122dd1adc14586e4035d7c14
🔍 Latest deploy log	https://app.netlify.com/sites/dynamic-faloodeh-e195d3/deploys/65960e2dbf38e900088ae8fc
😎 Deploy Preview	https://deploy-preview-27--dynamic-faloodeh-e195d3.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 configuration.