Copy edit for clarity and grammar

Made small edits to "Tips and Tricks" section.

website/templates/_description.html

@@ -11,7 +11,7 @@
       <ol>
         <li>Keep it short, and write each event as a part of a larger narrative.</li>
         <li>Pick stories that have a strong chronological narrative. It does not work well for stories that need to jump around in the timeline.</li>
-        <li>Include events that build up to major occurrences.<em>Not just the major events.</em></li>
+        <li>Include events that build up to major occurrences — <em>not just the major events.</em></li>
       </ol>
     </div>
     <div class="span6">