Add icepyx-gallery to the Pangeo Gallery

[salvis2]

Related to #1 .

The last step for setting up the gallery repo is to add it as a submodule to pangeo-gallery. This is done once we confirm that the notebooks are all building correctly. In the GitHub Action, we should see that all steps succeed except the last one, Trigger repository dispatch on Pangeo Gallery. Once that is the case, you can follow instructions in the link above to connect the repos. It may require that you re-run the last almost successful Action in this repo again.