Recommend using fences over indentation

See knatten#345.

templates/quiz/create.html

@@ -23,7 +23,7 @@ <h3>Please remember:</h3>
 
         <p><label for="id_answer">The output of this program is:</label> {{ form.answer }} {{ form.answer.errors }}<span class="help_text">Leave blank for questions with errors / undefined behavior</span></p>
 
-        <p><label for="id_explanation">Explanation: <span class="help_text">Please be clear and to the point. Please try to use correct terminology. Refer to the standard like this: "§[section.optional_subsections]¶optional_paragraph" (e.g. "§[over]" or "§[over.ics.list]¶6.2").  Use <a href="https://daringfireball.net/projects/markdown/syntax">markdown</a> for formatting, in particular wrap code in backticks like this: `int i`, or indent whole blocks with four spaces. Don't worry if you don't get the formatting perfect, a moderator will go over it before publishing. </span></label></p>
+        <p><label for="id_explanation">Explanation: <span class="help_text">Please be clear and to the point. Please try to use correct terminology. Refer to the standard like this: "§[section.optional_subsections]¶optional_paragraph" (e.g. "§[over]" or "§[over.ics.list]¶6.2").  Use <a href="https://daringfireball.net/projects/markdown/syntax">markdown</a> for formatting, in particular wrap code in backticks like this: `int i`, or surround whole blocks with fences (```). Don't worry if you don't get the formatting perfect, a moderator will go over it before publishing. </span></label></p>
         <div id="explanation_errors">{{ form.explanation.errors }}</div>
         <p>{{ form.explanation }}</p>