Add .add() to Vector

src/Vector.java

@@ -45,6 +45,12 @@ public class Vector {
         return new Vector(x + v.x, y + v.y, z + v.z);
     }
 
+    public void add(Vector v) {
+        this.x += v.x;
+        this.y += v.y;
+        this.z += v.z;
+    }
+
     /**
      * Returns the product of this vector and 'd'.
      */