C++: Fix qhelp formatting.

Author: geoffw0

cpp/ql/src/Likely Bugs/Likely Typos/IncorrectNotOperatorUsage.qhelp

@@ -16,9 +16,13 @@
 <p>Carefully inspect the flagged expressions. Consider the intent in the code logic, and decide whether it is necessary to change the not operator.</p>
 </recommendation>
 
+<example>
 <p>Here is an example of this issue and how it can be fixed:</p>
-<example><sample src="IncorrectNotOperatorUsage.cpp" /></example>
+
+<sample src="IncorrectNotOperatorUsage.cpp" />
+
 <p>In other cases, particularly when the expressions have <code>bool</code> type, the fix may instead be of the form <code>a &amp;&amp; !b</code></p>
+</example>
 
 <references>
   <li>