Re-organize left-side nav pane

[aliciakeyes]

in Docusaurus wrangles.io, we need to organize the navigation pane so it is useful to a user poking around wrangles.io.

new wrangles.io

1. mimic current wrangles.io?
2. some other path

@ebhills , any thoughts on how you'd like this navigation to flow? it's currently just a laundry list of all pages on the site.