Fix broken link in README

Author: Darksonn

README.md

@@ -21,7 +21,7 @@ The Rust build system has a Python script called `x.py` to bootstrap building
 the compiler. More information about it may be found by running `./x.py --help`
 or reading the [rustc guide][rustcguidebuild].
 
-[rustcguidebuild]: https://rust-lang.github.io/rustc-guide/how-to-build-and-run.html
+[rustcguidebuild]: https://rust-lang.github.io/rustc-guide/building/how-to-build-and-run.html
 
 ### Building on *nix
 1. Make sure you have installed the dependencies: