Fix "getting started" link

The previous link is 404.

Author: e00E

CONTRIBUTING.md

@@ -4,5 +4,5 @@ Thank you for your interest in contributing to Rust!
 
 To get started, read the [Getting Started] guide in the [rustc-dev-guide].
 
-[Getting Started]: https://rustc-dev-guide.rust-lang.org/getting-started.md
+[Getting Started]: https://rustc-dev-guide.rust-lang.org/getting-started.html
 [rustc-dev-guide]: https://rustc-dev-guide.rust-lang.org/

README.md

@@ -26,7 +26,7 @@ The Rust build system uses a Python script called `x.py` to build the compiler,
 which manages the bootstrapping process. More information about it can be found 
 by running `./x.py --help` or reading the [rustc dev guide][rustcguidebuild].
 
-[gettingstarted]: https://rustc-dev-guide.rust-lang.org/getting-started.md
+[gettingstarted]: https://rustc-dev-guide.rust-lang.org/getting-started.html
 [rustcguidebuild]: https://rustc-dev-guide.rust-lang.org/building/how-to-build-and-run.html
 
 ### Building on a Unix-like system