document new utils and change organization to match css

docs/utilities/position.md

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+---
+layout: docs
+title: Position
+group: utilities
+---
+
+Position utilities are helpful for quickly placing a component outside the normal document flow. Choose from a handful of fixed or sticky position classes as needed.
+
+### Fixed top
+
+Position an element at the top of the viewport, from edge to edge. Be sure you understand the ramifications of fixed position in your project; you may need to add aditional CSS.
+
+{% highlight html %}
+<div class="fixed-top">...</div>
+{% endhighlight %}
+
+### Fixed bottom
+
+Position an element at the bottom of the viewport, from edge to edge. Be sure you understand the ramifications of fixed position in your project; you may need to add aditional CSS.
+
+{% highlight html %}
+<div class="fixed-bottom">...</div>
+{% endhighlight %}
+
+### Sticky top
+
+Position an element at the top of the viewport, from edge to edge, but only after you scroll past it. The `.sticky-top` utility uses CSS's `position: sticky`, which isn't fully supported in all browsers.
+
+{% highlight html %}
+<div class="sticky-top">...</div>
+{% endhighlight %}