Prompt for what to initialize, update instead of going through everything #43

We might consider prompting to initialize or update more advanced or otherwise optional fields like pathTemplate. Correct me if I'm wrong, but I think the original idea is that for many SSGs the default just works but for my Jekyll-based site - with a little customization, admittedly, of my posts' path template - I needed more control. But how many people would?

I'm thinking of something like the GitHub CLI like when creating an issue or PR: it requires at least a title, lets you specify an optional body, and then asks if you want to change anything else. If you affirm, it prompts with a selection of what you can change. I'm not suggesting it has to get all fancy - they are relying on Charmbracelet (Go) for most of that, which has a lot of built-in UX, but maybe just even letting people hit Enter on an item, set it, then return to the list to repeat or save could suffice.

I appreciate that with these advanced scenarios, maybe allowing them to edit sequoia.json is sufficient. But in that case, we might show a final message about editing sequoia.json - as a file path for ease - along with a link to https://sequoia.pub/config that most modern terminals will effectively wrap in an OSC8.