Added cart to docs

Author: georgebutter

docs/_config.yml

@@ -39,6 +39,9 @@ nav:
     url: '#helper-classes'
   - title: Sass mixins
     url: '#sass-mixins'
+  - title: 'Cart'
+    url: '#cart'
+    
 # Collections ================================================================
 collections:
   documentation:

docs/_documentation/cart.md

@@ -0,0 +1,25 @@
+---
+title:  "Cartfox"
+handle: "cart"
+category: "cart"
+---
+Concrete uses [Cartfox🛒🦊](https://github.com/Elkfox/Cartfox) for all things ajax-y and cart-ish. If you're developing with Slate you can find an un-minified version in `/src/scripts/vendor/concrete.cart.js`. Upon deployment this will be minified into the `vendor.js`.
+
+As you can see in the `/layout/theme.liquid` Cartfox is initialized here using Concrete's default elemnts for selectors. if you wish to changes class names or apply different selectors you can do so here.
+
+{% highlight javascript %}
+  var cart;
+  $(document).ready(function() {
+    cart = new Cartfox.Cart({{ cart | json }}, {
+      addItem: '#AddToCart',
+      cartItemCount: "#CartItemCount",
+      cartTotal: "#CartTotal, .cart-total",
+      decreaseQuantity: "[data-minus-one]",
+      increaseQuantity: "[data-plus-one]",
+      itemQuantity: '.item-qty',
+      removeItem: '.removeItem',
+      emptyTemplate: '#CartTemplate',
+      itemsContainer: '#PopupCart .items'
+    });
+  });
+{% endhighlight %}