GUACAMOLE-747: Provide example branding extension.

doc/guacamole-branding-example/html/warning.html

@@ -0,0 +1,8 @@
+<!-- Sets up a dialog box that will be inserted immediately after the "version"
+     element. -->
+<meta name="after" content=".version" />
+
+<!-- An HTML div that has a class of "warning", pluss the other classes that
+     will be applied from above. -->
+<div class="warning">Beware of entering Saturn's gravitational field.
+    Few who enter it ever escape.</div>