Adding note to summing fields

Author: erikvansebille

docs/user_guide/examples/explanation_kernelloop.md

@@ -42,6 +42,10 @@ Besides having commutable Kernels, the main advantage of this implementation is
 
 Below is a simple example of some particles at the surface of the ocean. We create an idealised zonal wind flow that will "push" a particle that is already affected by the surface currents. The Kernel loop ensures that these two forces act at the same time and location.
 
+```{note}
+Advecting particles by a combination of flow fields can be done with two separate kernels, as is shown below. However, it can also be done by summing the fields directly using `xarray` operations - provided the fields are defined on the same grid and have compatible dimensions. See the [summing fields tutorial](tutorial_summingfields.ipynb) for an example of that approach.
+```
+
 ```{code-cell}
 :tags: [hide-output]
 import matplotlib.pyplot as plt