Document helpful testing techniques that can boost quality of life for individual projects

Things like
- Custom QUnit checkboxes!!
- Assigning getSettledState / getPendingWaiterState to `window` (so you can see what's holding up your test _live_!)
- why / how is a property changing? (example: observing an effect ruin your day) -- intercept it with a getter/setter pair _or_ just put a breakpoint in source (node_modules chunk/vendor/etc) if the code already has a setter (like if you need to figure out what is setting an ember-data `@attr` (my day today, oof :see_no_evil: ))
- `macroCondition(....) ` (test-only or dev-only code)