Update security.rst

Mario A. Alvarez Garcia · Mario A. Alvarez Garcia · commit c8c093ab6b82 · 2014-03-04T15:43:53.000-05:00
I'm not a native speaker but I think that it sounds better by adding that before the word `start`.
diff --git a/book/security.rst b/book/security.rst
@@ -20,7 +20,7 @@ perform a certain action.
 .. image:: /images/book/security_authentication_authorization.png
    :align: center
 
-Since the best way to learn is to see an example, start by securing your
+Since the best way to learn is to see an example, let's start by securing your
 application with HTTP Basic authentication.
 
 .. note::
