Okta-Specific README Clarification

[favorable-mutation]

The section of the README dealing with setup for Okta can be a bit difficult to understand if you don't know exactly what you're looking for; this PR clarifies those instructions somewhat and links to a page with an image replicating what you should be looking for in the Okta Web UI.

There are also some elements of the README that should probably be code-formatted. This PR adds double backticks around such elements that only had single backticks, allowing GitHub to parse them as inline code-formatted.