Problem

In the course of working on #262, I found a couple of small issues with the quickstart guide: the quickstart-specific suggested OAuth callback URLs in the google & okta provider setup docs were incomplete.

Solution

FIrst, fix the suggested URLs. I also made a few more invasive/opinionated wording/structure changes to the quickstart guide itself, if these changes do not seem like an improvement to y'all I will revert them!