add a rustfmt detail to CONTRIBUTING.md

diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index f111ed3cde38ba5e81ac24d91bd62291e196c754..b05c793064b1ff261ec6df7e0d7bd0dd4aead764 100644 (file)
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -82,8 +82,8 @@ installed locally, ignore the cross-compile test failures or disable them by
 using `CFG_DISABLE_CROSS_TESTS=1 cargo test`. Note that some tests are enabled
 only on `nightly` toolchain. If you can, test both toolchains.
 * All code changes are expected to comply with the formatting suggested by `rustfmt`.
-You can use `rustup component add rustfmt-preview` to install `rustfmt` and use
-`cargo fmt` on the changed files to automatically format your code.
+You can use `rustup +stable component add rustfmt-preview` to install `rustfmt` and use
+`rustfmt +stable --skip-children $FILE` on the changed files to automatically format your code.
 * Push your commits to GitHub and create a pull request against Cargo's
 `master` branch.