Add youtube usage example

Kwpolska · Kwpolska · commit 91c5c088a083 · 2016-09-18T19:14:16.000+02:00
Signed-off-by: Chris Warrick &lt;kwpolska@gmail.com&gt;
diff --git a/docs/manual.txt b/docs/manual.txt
@@ -2009,7 +2009,12 @@ Once you have that, all you need to do is:
     .. youtube:: 8N_tupPBtWQ
 
 Supported options: ``height``, ``width``, ``align`` (one of ``left``,
-``center``, ``right``) — all are optional.
+``center``, ``right``) — all are optional. Example:
+
+.. code:: restructuredtext
+
+    .. youtube:: 8N_tupPBtWQ
+       :align: center
 
 Vimeo
 ~~~~~
