Add example for diff between assert true and equal

On a patch someone said it was not clear to them what the difference
was. So I made an example, I thought it may be useful to have this in the
docmentation for future reference, for other people.

Change-Id: I2825d66ebae5681162e4a868b1083bdbe7f0917a

doc/source/contributing/minor-code-changes.rst

@@ -32,6 +32,29 @@ We're not saying that such changes can never be made, we're just saying that
 each change must be accompanied by an explanation of why the weaker test is
 adequate for what's being tested.
 
+Just to make this a bit clearer it can be shown using the following
+example, comment out the lines in the runTest method alternatively::
+
+  import unittest
+
+  class MyTestCase(unittest.TestCase):
+      def setUp(self):
+          pass
+
+  class Tests(MyTestCase):
+      def runTest(self):
+          self.assertTrue('True')
+          self.assertTrue(True)
+          self.assertEqual(True, 'True')
+
+To run this use::
+
+  python -m testtools.run test.py
+
+Also mentioned within the unittests documentation_.
+
+.. _documentation: https://docs.python.org/3/library/unittest.html#unittest.TestCase.assertTrue
+
 LOG.warn to LOG.warning
 -----------------------