Added Write a Toy VPN in Rust, In the Readme.md

[biomathcode]

Added Write a Toy VPN in Rust Tutorial Link, in the Readme.md

Description

Write a Toy VPN in rust is a great Tutorial/Project based learning resources.

Motivation and Context

Learn how VPN work and also how to implement it yourself in rust. It's a step by step tutorial with code provided by the author. Also, include further reads for the reader.

How Has This Been Tested?

I read it myself.

Types of changes

• [ ] Content Update (change which fixes an issue or updates an already existing submission)
• [x] New Article (change which adds functionality)
• [ ] Documentation change

Checklist:

• [x] My code follows the code style of this project.
• [x] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.
• [x] I have made checks to ensure URLs and other resources are valid