bin: Add script to run rustfmt against all workspaces

Add a script to run `cargo fmt` on all Rust code contained in crosvm.
This is different from `cargo fmt --all` which formats multiple crates
but a single workspace only. Crosvm consists of multiple workspaces.

Usage:

    $ bin/fmt

To print a diff and exit 1 if code is not formatted, but without
changing any files, use:

    $ bin/fmt --check

TEST=those commands
TEST=local kokoro

Change-Id: I4194509ad3a1bbc829c4b1069d54d940b927113b
Reviewed-on: https://chromium-review.googlesource.com/1477498
Commit-Ready: David Tolnay <dtolnay@chromium.org>
Tested-by: David Tolnay <dtolnay@chromium.org>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Zach Reizner <zachr@chromium.org>

1 files changed, 5 insertions, 2 deletions

diff --git a/README.md b/README.md
index bde48ea..8c590d9 100644
--- a/README.md
+++ b/README.md
@@ -138,8 +138,11 @@ for each architecture. See `build_test -h` for more information.
 
 #### `rustfmt`
 
-All code should be formatted with `rustfmt`.  Run `cargo fmt --all` to autoformat
-your code before checking in a change.
+All code should be formatted with `rustfmt`. We have a script that applies
+rustfmt to all Rust code in the crosvm repo: please run `bin/fmt` before
+checking in a change. This is different from `cargo fmt --all` which formats
+multiple crates but a single workspace only; crosvm consists of multiple
+workspaces.
 
 #### Dependencies