[REVIEW] Add citation for python modules

[bnubald]

Based on review feedback:

• [REVIEW] Sea ice forecasting using the IceNet library eds-book/notebooks-reviews#7

• [REVIEW] Sea ice forecasting using the IceNet library eds-book/notebooks-reviews#7

• Add citation for python software packages.

By weiji14:

[ ] All mentioned software should be formally and consistently cited wherever possible.

Missing citations for cartopy, matplotlib, xarray, etc.