Add Rust Trends newsletter edition 70 to twir

Author: Rust-Trends

draft/2025-09-17-this-week-in-rust.md

@@ -43,6 +43,8 @@ and just ask the editors to select the category.
 
 ### Newsletters
 
+* [Rust Trends Issue #70: Foundation Moves and Performance Breakthroughs](https://rust-trends.com/newsletter/rust-foundation-performance-breakthroughs-2025)
+
 ### Project/Tooling Updates
 
 ### Observations/Thoughts