Added nice example

example.py

+def add(a, b):
+    return a + b
+
+
+def test_add():
+    assert add(2, 3) == 5
+    assert add('space', 'ship') == 'spaceship'
+
+
+def subtract(a, b):
+    return a + b  # <--- fix this in step 8
+
+
+# uncomment the following test in step 5
+#def test_subtract():
+#    assert subtract(2, 3) == -1
\ No newline at end of file