(doc) Point readers to how to run acceptance tests
(doc) Update rspec examples to show desired style

There are a couple stylistic points about rspec that we need to follow:

  * be explicit
  * say what it does

"Be explicity" means that we use `before :each` instead of `before`.
This lowers the amount of mental energy that a reader needs to use to
understand how things will fit together.

"Say what it does" means that the examples read as declarations of what
the system under test *does*. A writer must avoid wish-washy words such
as "should" or "could" or "may". Instead state exactly what the system
does in that situation.