Fix the CONTRIBUTING doc for the new formatting

CONTRIBUTING.md

@@ -8,12 +8,13 @@
 
 #### Installing rustfmt
 
-You can run `rustfmt` with Rust 1.24 and above.
+You must install a very recent version of `rustfmt` through rust nightly
 
 To install: 
 
 ```
-rustup component add rustfmt
+rustup toolchain install nightly-x86_64-unknown-linux-gnu
+rustup component add rustfmt --toolchain nightly
 ```
 
 #### Usage 
@@ -21,14 +22,24 @@ rustup component add rustfmt
 To run on Diplonat, launch the following in the root directory:
 
 ```
-cargo fmt --all
+cargo +nightly fmt
 ``` 
 
-This will format the whole repository using the settigs defined in [`.rustfmt.toml`](./.rustfmt.toml): soft tabs of 2 spaces.
+This will format the whole repository using the settigs defined in [`.rustfmt.toml`](./.rustfmt.toml).
 
 #### Auto-format code
 
 You can automate formatting in a number of ways:
 
-* [Setup your IDE to use `rustfmt`](https://github.com/rust-lang/rustfmt#running-rustfmt-from-your-editor).
-* Setup a git hook to run `rustfmt` before each commit.
+[Setup your IDE to use `rustfmt`](https://github.com/rust-lang/rustfmt#running-rustfmt-from-your-editor).
+
+Setup a git hook to run `rustfmt` before each commit:
+
+```bash
+cat <<EOF > .git/hooks/pre-commit
+#!/bin/bash
+
+cargo +nightly fmt
+EOF
+chmod +x .git/hooks/pre-commit
+```