content: Add thoughts about Rust code formatting

This is from the works of
[firecracker](https://github.com/firecracker-microvm/firecracker/), by
analyzing how they format Rust code.

Signed-off-by: Ruoqing He <heruoqing@iscas.ac.cn>

Author: RuoqingHe

src/repo-management/firecracker/rustfmt.md

@@ -0,0 +1,14 @@
+# How Firecracker Format Their Rust Code
+
+Like most Rust projects,
+[Firecracker](https://github.com/firecracker-microvm/firecracker/) uses
+`cargo fmt` (namely `rustfmt`) to format Rust code.
+
+This rule is applied bu executing the `pre-commit` shell script, and enforced in
+their CI.
+
+## pre-commit Script
+
+This script lints every staged file, as of `.rs`s, it apply `cargo fmt` on them.
+The command directly formats that file instead of produce differences
+before/after format.