Add factorial examples in Rust

03_recursion/rust/03_factorial/src/main.rs

@@ -0,0 +1,11 @@
+fn fact(x: u32) -> u32 {
+    if x == 1 {
+        return 1;
+    }
+
+    return x * fact(x - 1);
+}
+
+fn main() {
+    println!("{}", fact(3));
+}