move containers to layout section

docs/layout/containers.md

@@ -0,0 +1,24 @@
+---
+layout: page
+title: Containers
+---
+
+Bootstrap requires a containing element to wrap site contents and house our grid system. You may choose from one of two containers—fixed width or fluid width—to use in your projects.
+
+Containers *can* be nested, but be aware that most layouts don't require it.
+
+Use `.container` for a responsive fixed width container. This will center content withing the viewport and apply the appropriate `width` for a given device size.
+
+{% highlight html %}
+<div class="container">
+  ...
+</div>
+{% endhighlight %}
+
+Use `.container-fluid` for a full width container, spanning the entire width of the viewport.
+
+{% highlight html %}
+<div class="container-fluid">
+  ...
+</div>
+{% endhighlight %}