add how-to page(s)

[JonasDoesThings]

this issue is to track progress & content ideas for adding a how-to page / user guide. send me additional topics to cover

topics:

• basic sankey diagram

  • [x] comments
  • [x] auto-calculated flows ([?] operator)
  • [ ] important settings like value suffix, decimal related, canvas size, etc.
  • [ ] sharing / exporting
  • [ ] importing

• advanced(-ish) usage

  • [x] specifying custom colors
  • [ ] positions array? (idk if we want to include this, it's implemented highly anti-ux tbh)

• small tips & tricks / hacks

  • [ ] hide text: -> change font size to 0

• example gallery

  • [ ] highlight real-world sankey diagrams?

• [ ] add ~"go back" button to navbar in subpages?

[JonasDoesThings]

in-part released to prod with v1.4.0 more content will follow with coming releases