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

[Andrew Donnellan]

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Update the link to clippy and get rid of outdated installation information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>
---
 CONTRIBUTING.md | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 8d040725f3ca..a6daa1feff25 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -24,14 +24,15 @@ relevant. Specifically, pay attention to:
  * Separating logical changes into separate patches
  * Plain-text patches, as generated by `git send-email`
 
-We like to follow the [Rust Guidelines](https://aturon.github.io/)
-where possible - patches to fix existing non-compliant code are
-welcome!
-
-If you're using a nightly Rust toolchain, you can use the
-[clippy](https://github.com/Manishearth/rust-clippy) linter: `cargo
-+nightly install clippy` to install, and `cargo +nightly clippy` to
-run.
+We like to follow the [Rust Style
+Guide](https://github.com/rust-lang-nursery/fmt-rfcs/blob/master/guide/guide.md)
+wherever possible - patches to fix any non-compliant code are welcome!
+The `setup_rustfmt_hook.sh` script in the root of the repository will
+set up a local pre-commit hook that runs `rustfmt` over your changes -
+we strongly recommend using this.
+
+We also recommend using the
+[clippy](https://github.com/rust-lang-nursery/rust-clippy) linter.
 
 When your patch involves creating a new file, where possible please
 use a header along the lines of:
-- 
2.11.0