Add more mesh creation examples to docs

[lukem12345]

Currently, CombinatorialSpaces and Decapodes demonstrate mesh creation/ import throughout the tests and docs, with a catalogue here. CombinatorialSpaces has an API for natively creating meshes by gluing triangles, but for complex mesh creation use cases, we advise users to create their mesh in any software of their choice, and import via .obj files.

However, modelers who are not used to creating a mesh in any tool find it hard to get started.

So, we should demonstrate some recommended ways of creating meshes that users can copy, so they are less overwhelmed with choice. We should also point to external walkthroughs on how to create .obj files.

We would especially benefit from further tetrahedral mesh/ "tetramesh"/ "hypermesh" examples. A test currently demonstrates how to use TetGen.jl on a Meshes.jl quadrilateral, copied from the TetGen README.