Tell problem solver how long they should wait before resetting the servo

Author: Alan Shaw

exercises/servo_wave/problem.md

@@ -1,10 +1,10 @@
 __Make a servo wave at you for 3 seconds, stop, and return to center.__
 
-- Create a new `Servo` instance attached to pin 9.
-- Use `servo.sweep` to rotate between 0˚ and 180˚.
-- Use `board.wait` to schedule a 'reset' callback.
-- The 'reset' callback should `stop` and `center` the servo.
-- Check the docs to see how to bring it back into line.
+- Create a new `Servo` instance attached to pin 9
+- Use `servo.sweep` to rotate between 0˚ and 180˚
+- Use `board.wait` to schedule a 'reset' callback after **3 seconds**
+- The 'reset' callback should `stop` and `center` the servo
+- Check the docs to see how to bring it back into line
 
 ## Boilerplate
 ```js