update README for a simple instruction and preview image

Author: zbryikt

README.md

@@ -1,11 +1,34 @@
 loading.css
 ------------------
 
+![loading.css preview](https://github.com/loadingio/loading.css/blob/master/preview.gif?raw=true)
+
 40+ Handcrafted CSS animations dedicated for your loaders. All animations here are designed for repeatable, infinitely playing. online demo could be found here: [loading.css](https://loading.io/animation/)
 
 loading.css is released together with a handy tool which build GIFs from CSS animation for us. Check [Custom GIF Generator](https://loading.io/animation/icon/) to see how it works.
 
 
+
+Usage
+==================
+
+1. download and include [loading.css](https://raw.githubusercontent.com/loadingio/loading.css/master/dist/loading.css):
+
+
+    <link rel="stylesheet" type="text/css" href="loading.css"/>
+
+
+2. check [loading.css animation gallery](https://loading.io/animation/) for the name of animations you want to use. for example, `ld-spin`.
+
+3. use the name as css class on the element you want to animate:
+
+
+    <div class="ld ld-spin"></div>
+
+
+4. for more information, check out [loading.css animation documentation](https://loading.io/animation/).
+
+
 LICENSE
 ==================