Add hint to variable shadowing for variables3.rs

[torbenj]

I think a nice addition to variables3.rs would be to also mention variable shadowing as it also solves the exercise and also gets explained in chapter 3 of the book (https://doc.rust-lang.org/book/ch03-01-variables-and-mutability.html)

Any opinions on that one?

[AbdouSeck]

Hi @torbenj, that sounds like a terrific idea! Want to add that to variables3.rs or even make a variables5.rs file where you highlight exactly what's expected?

Thank you,

Abdou

[torbenj]

Yeah I'll give it a try