Add docs for prettify.

site/dev/tools/markdown.md

 Markdown
 ========
 
 This site can handle normal MarkDown and many common extensions. To learn
 how the following is done please see the [source for this page](./markdown.md).
 Any file you put under `/site/` that has the extension `.md` will be processed
 as MarkDown. All other files will be served directly. For example, images
 can be added and they will be served correctly and referenced from within MarkDown files.
 
 Some Example MarkDown
@@ skipping 24 matching lines @@
     |  +----------------+  |
     |                      |
 +---v---+              +---v---+
 |       |              |       |
 |  Yes  |              |  No   |
 |       |              |       |
 +-------+              +-------+
 
 ~~~~
 
-Format code snippets or other preformatted text.
+Format code snippets or other preformatted text. Just surround the code
+with `~~~~`. You can also trigger syntax highlighting by putting in
+the following HTML comment before the code section:
 
+    <!--?prettify?-->
+
+
+<!--?prettify?-->
 ~~~~
 class SK_API SkPaint {
 public:
     SkPaint();
     SkPaint(const SkPaint& paint);
     ~SkPaint();
 
     SkPaint& operator=(const SkPaint&);
 ~~~~
 
+
 Tables
 
   Name    | Value    | Summary
   --------|----------|--------
   A       | 27       |  yes
   B       | 23       |  no
 
 
 There are also inline styles for *emphasis*, **bold**,
 ~~strikethrough~~, and `inline code`. Also small fractions,
@@ skipping 290 matching lines @@
 
 Output:
 
     <p>If you want your page to validate under XHTML 1.0 Strict,
     you've got to put paragraph tags in your blockquotes:</p>
     
     <pre><code>&lt;blockquote&gt;
         &lt;p&gt;For example.&lt;/p&gt;
     &lt;/blockquote&gt;
     </code></pre>