doc: add 4D Fudge example

01.workspace/oxidice_lib/examples/roll_4D_Fudge.rs

@@ -0,0 +1,7 @@
+use oxidice_lib::dice::*;
+
+fn main() {
+    let roll = Handful::grab_range(4, -1..=1).roll();
+    let sum = roll.clone().sum().unwrap();
+    println!("{} -> {}", roll, sum);
+}