Update instructions

README.md

@@ -7,15 +7,15 @@
 
 This kata complements [Clean Code: Advanced TDD, Ep. 23](https://cleancoders.com/episode/clean-code-episode-23-p1).
 
-This repository contains an exercise designed to improve your skills in
+This repository contains two exercises designed to improve your skills in
 test-driven development. It represents code you inherited from a legacy code
 base.
 
 As a first step, try to get some kind of test in place before you change the
 class at all. If the tests are hard to write, is that because of the problems
 with SOLID principles?
 
-### Exercise
+### Exercise 1
 
 Write the unit tests for the `Alarm` class. The `Alarm` class is designed to
 monitor tire pressure and set an alarm if the pressure falls outside of the
@@ -24,6 +24,20 @@ expected range.
 The `Sensor` class provided for the exercise simulates the behaviour of a real
 tire sensor, providing random but realistic values.
 
+You can choose to use stubs, mocks, or none at all. If you do, you are free to
+use the mocking tool that you prefer.
+
+> **Note**
+>
+> If you decide to use mocks, we recommend using the
+> [unittest.mock](https://docs.python.org/3/library/unittest.mock.html)
+> mock object library.
+
+### Exercise 2
+
+Use one of the mocking patterns: Self-Shunt, Test-Specific Subclass, or Humble
+Object. If you used one of them already, use another one.
+
 ## Usage
 
 You can import this project into [Replit](https://replit.com), and it will