[snowpatch] [PATCH v2 1/6] CONTRIBUTING.md: Update references, add rustfmt information

[Russell Currey]

On Mon, 2018-07-23 at 17:04 +1000, Andrew Donnellan wrote:
> The Rust Guidelines have disappeared, so replace that with a link to
> the
> current Rust Style Guide.
> 
> Document the new rustfmt git pre-commit hook.
> 
> Update the link to clippy and get rid of outdated installation
> information
> that's better documented in the clippy repo anyway.
> 
> Signed-off-by: Andrew Donnellan <andrew.donnellan at au1.ibm.com>

Series applied to master (I almost forgot how), thanks mate.