Better thumbnails for gallery examples

[charlesbmi]

Issue

As an open-source software user, I often look at the example gallery to get a quick glimpse of a package's capabilities. Many NDK examples currently lack an image, or their images look very similar to one another, so it is unclear (at first glance) how the examples differ.

Current example gallery view:

We could do 2 things:

• Customize the thumbnail for some examples: https://smarie.github.io/mkdocs-gallery/generated/gallery/plot_4b_provide_thumbnail/
  • Currently, the thumbnails default to the first image produced by the IPython script
• Animate thumbnails for some of the examples that produce FuncAnimation: https://smarie.github.io/mkdocs-gallery/generated/gallery/plot_8_animations/