Fix images on markdown pages

website/source/docs/modules/usage.html.markdown.erb

@@ -91,13 +91,13 @@ For example, with a configuration similar to what we've built above, here
 is what the graph output looks like by default:
 
 <div class="center">
-<img src="/images/docs/module_graph.png">
+<%= image_tag 'docs/module_graph.png' %>
 </div>
 
 But if we set `-module-depth=-1`, the graph will look like this:
 
 <div class="center">
-<img src="/images/docs/module_graph_expand.png">
+<%= image_tag 'docs/module_graph_expand.png' %>
 </div>
 
 Other commands work similarly with modules. Note that the `-module-depth`