I am sorry for not being familiar with programing at all. However, jupyter-polymake may require JuPyMake module, I think. If the module is not installed, Jupyter notebook can not connect to polymake (I installed polymake from the source to my macOS 10.14.5 as in Installation instruction).
How about add JuPyMake in the Requirements section of the README? Or I should make a Pull Requiest?
Thanks,