Atlas review - Reference grids

[huard]

• [x] README: The figures colorbar should include a label.
• [x] README: ERA5 land sea mask is not mentioned.
• [x] scripts/ does not seem to cover the ERA5 land sea mask.

[jesusff]

Thank you for the review. All comments have been taken into account. The colorbar no longer applies since the figure shows now the binary masks.