githooks: add pre-commit hook with dry `cargo fmt`

.githooks/pre-commit

@@ -0,0 +1,11 @@
+#!/bin/bash
+
+diff=$(cargo fmt -- --check)
+result=$?
+
+if [ ${result} -ne 0 ]; then
+    echo "There are some code formatting issues, run `cargo fmt` first."
+    exit 1
+fi
+
+exit 0