Contributing: add 'Getting started with Rust kernel development' section

There is no link to the Rust kernel documentation in the Contributing
page. We do have it at the top of the links in the sidebar, but that
may not be obvious. Therefore, add a section on getting started with
Rust kernel development that points to it.

Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: ojeda

src/Contributing.md

@@ -48,6 +48,12 @@ There are many ways to contribute to the Rust support in the kernel:
 
   - Helping others on Zulip. For instance, getting them started with the Rust support in the kernel.
 
+## Getting started with Rust kernel development
+
+Please read the documentation under [`Documentation/rust`](https://docs.kernel.org/rust/). In particular, the [Quick Start guide](https://docs.kernel.org/rust/quick-start.html).
+
+Reading the rest of this website is also recommended.
+
 ## The Rust subsystem
 
 The Rust subsystem takes care of the core Rust abstractions as well as the general infrastructure for Rust in the kernel. It is a bit special in that it potentially intersects with every other subsystem in the kernel, especially in the beginning of the Rust support in the kernel.