add trait from<u128> to Num

src/num.rs

@@ -22,4 +22,10 @@ impl std::ops::Mul<u128> for Num {
     fn mul(self, rhs: u128) -> Self::Output {
         self.number * rhs
     }
+}
+
+impl From<u128> for Num {
+    fn from(number: u128) -> Self {
+        Num { number }
+    }
 }