Add rust resource (#8533)

* Update what-is-rust.md

Added one article to https://doc.rust-lang.org/stable/rust-by-example/index.html

* Update title

src/data/roadmaps/rust/content/introduction/what-is-rust.md

@@ -6,3 +6,4 @@ Visit the following resources to learn more:
 
 - [@video@What is Rust?](https://www.youtube.com/watch?v=R33h77nrMqc)
 - [@feed@Explore top posts about Rust](https://app.daily.dev/tags/rust?ref=roadmapsh)
+- [@official@Rust by example](https://doc.rust-lang.org/stable/rust-by-example/index.html)