[scikit-image] Comparison of watershed implementations

[Stefan van der Walt]

I wish the authors also compared accuracy, but here are their
performance benchmarks.  No surprises :)

https://www.mdpi.com/2313-433X/4/10/123/pdf

"An Overview of Watershed Algorithm Implementations in Open Source Libraries",
J. Imaging 2018, 4(10), 123; https://doi.org/10.3390/jimaging4100123,
Anton S. Kornilov and Ilia V. Safonov.

Best regards,
Stéfan