[#78] Updated readme to add wait best practice recommendation that was given by Kent in issue 78.

Author: RyanAtViceSoftware

.idea/inspectionProfiles/Project_Default.xml

@@ -374,6 +374,8 @@ The default `interval` is `50ms`. However it will run your callback immediately
 on the next tick of the event loop (in a `setTimeout`) before starting the
 intervals.
 
+> NOTE: `wait`'s callback can be called many times and because of this you should use as few `wait` calls as possible in each test and put minimum amount of code that absolutely needs to be waited on inside each `wait`'s `callback`. This will help your tests run faster and can avoid unnecessary runtime complexity. 
+
 ### `waitForElement`
 
 See [dom-testing-library#waitForElement](https://github.com/kentcdodds/dom-testing-library#waitforelement)