New "create a new board" vignette

[juliasilge]

Closes #737 as well as #481

I got a start on this draft while working on #749 and used the Google Drive board as the example. It's a pretty good example, mostly because the googledrive R package is so nice.

One thing this vignette highlights is that a lot of functions needed to create these methods are internal, like version_setup(), check_pin_exists(), and so forth, are all unexported. Should we export them? Or show them being used like pins:::check_pin_exists() in this vignette?