add markdown toc stuff

docs/components/modal.md

@@ -5,6 +5,11 @@ title: Modal
 
 Modals are streamlined, but flexible, dialog prompts with the minimum required functionality and smart defaults.
 
+## Contents
+
+* Will be replaced with the ToC, excluding the "Contents" header
+{:toc}
+
 **Due to how HTML5 defines its semantics, the `autofocus` HTML attribute has no effect in Bootstrap modals.** To achieve the same effect, use some custom JavaScript:
 
 {% highlight js %}