add todo for future non +y propagation direction

Author: PrometheusPi

lib/python/picongpu/picmi/gaussian_laser.py

@@ -138,6 +138,8 @@ def get_as_pypicongpu(self) -> laser.GaussianLaser:
             it using a huygens surface in the box, centroid_y <= 0"
         # @todo implement check that laser field strength sufficiently small
         # at simulation box boundary
+        # @todo extend this to other propagation directions than +y
+
 
         # check polarization vector normalization