Update posts/2021-07-29-Rust-1.54.0.md

Co-authored-by: XAMPPRocky <4464295+XAMPPRocky@users.noreply.github.com>

Author: Mark-Simulacrum

posts/2021-07-29-Rust-1.54.0.md

@@ -22,7 +22,7 @@ from the appropriate page on our website, and check out the
 [detailed release notes for 1.54.0][notes] on GitHub.
 
 [install]: https://www.rust-lang.org/install.html
-[notes]: XXX
+[notes]: https://github.com/rust-lang/rust/blob/master/RELEASES.md#version-1540-2021-07-29
 
 ## What's in 1.54.0 stable