[ENH] add examples, flesh out main page

[36000]

No description provided.

[36000]

@arokem what do you think about these changes? you can access the built website from the artifacts of the circleci run:

https://github.com/tractometry/tractometry.github.io/actions/runs/15425517911

[arokem]

Looks great! One small thing is that I read the icon that appears next to the tutorial titles as "download this" and I expect something to save onto my computer when I click that. I wonder whether that would confuse users as well?

[36000]

I re-organized the examples into their own section. the main page looks the same, but you can also go into the examples section and use the navigation bar. also, the examples are now embedded into the website's pages