public Quaternion add(Quaternion q) {
        return new Quaternion(x + q.x, y + q.y, z + q.z, w + q.w);
    }
Adds the argument and returns the sum as a new instance. The current
instance is unaffected.

<p>Seldom used. To combine rotations, use
{@link #mult(com.jme3.math.Quaternion)} instead of this method.

@param q the quaternion to add (not null, unaffected)
@return a new Quaternion
jme3-core/src/main/java/com/jme3/math/Quaternion.java