Add usage example in the docstring.

dash_core_components/LogoutButton.py

@@ -6,6 +6,26 @@
 class LogoutButton(Component):
     """A LogoutButton component.
 Logout button to submit a form post request to the `logout_url` prop.
+Usage is intended for dash-deployment-server authentication.
+
+DDS usage:
+
+`dcc.LogoutButton(logout_url=os.getenv('DASH_LOGOUT_URL'))`
+
+Custom usage:
+
+- Implement a login mechanism.
+- Create a flask route with a post method handler.
+`@app.server.route('/logout', methods=['POST'])`
+  - The logout route should perform what's necessary for the user to logout.
+  - If you store the session in a cookie, clear the cookie:
+  `rep = flask.Response(); rep.set_cookie('session', '', expires=0)`
+
+- Create a logout button component and assign it the logout_url
+`dcc.LogoutButton(logout_url='/logout')`
+
+See https://dash.plot.ly/dash-core-components/logout_button
+for more documentation and examples.
 
 Keyword arguments:
 - id (string; optional): Id of the button.