Add new article to "Rust Walkthroughs"

This is an introductory article to the concept of "Subtyping and Variance". Let me know if the section is okay :)

Author: marioortizmanero

draft/2024-09-18-this-week-in-rust.md

@@ -41,6 +41,8 @@ and just ask the editors to select the category.
 
 ### Rust Walkthroughs
 
+- [Blindsided by Rust's Subtyping and Variance](https://nullderef.com/blog/rust-variance/)
+
 ### Research
 
 ### Miscellaneous