Document formats for examples

[cgarling]

Currently going with jupyter notebooks because they're easy and render natively on github, but doesn't lend well to inclusion on the docs pages. Might be better to go with something like Literate.jl or Weave.jl that is more explicitly designed to support conversion to easily hostable formats.

[cgarling]

This issue might be of help: https://discourse.julialang.org/t/deploy-literate-non-html-files-with-documenter/66031

[cgarling]

Now that the repo is public, we can benefit from the rendering service of nbviewer.org, see
https://nbviewer.org/github/cgarling/StarFormationHistories.jl/blob/main/examples/fitting1.ipynb