Restructure the README further.

* Remove the references section, as it wasn't cross-linked (though it
  seems worthy to re-add later)
* Remove the TOC -- GitHub automatically generates a navigable one when
  rendering the README, and it's annoying to maintain a manual one
* Re-order the sections slightly, though they likely still can be
  improved
* Compress a few cases of the same information being repeated
* Write out the test runner algorithm in more pseudocode-y style
* Add a basic note about `refRemote` needing the schema catalog, and
  call out invariants separate from assumptions

Author: Julian