Add narrative and explanation in Generating Meshes

[philippjfr]

The Generating Meshes notebook currently has no explanatory text and display a pipeline which is of course not usable on the static website. Therefore it doesn't actually demonstrate what the notebook is meant to be about which is to generate meshes.

[kcpevey]

One alternative could be to move the meshing page to the end of the grabcut notebook.

The grabcut-to-mesh dashboard in AdhUI shows the deployable app version https://github.com/erdc/AdhUI/blob/master/docs/Dashboards/Grabcut_Mesher.ipynb

We can't migrate that to earthsim due to circular dependencies though. We don't have a way of hosting it, otherwise a link to that pipepline app might be beneficial in the earthsim docs.