create documentation for how extend BaseAnimation

Author: dielduarte

README.md

@@ -65,6 +65,40 @@ Example:
 
 See all examples [here](https://dielduarte.github.io/animate-css-styled-components/)
 
+## How to create custom styled animations
+
+You can import BaseAnimation component and create your custom animation
+
+Example:
+
+```
+  import { BaseAnimation } from 'animate-css-styled-components';
+  
+  //create your custom animation
+  const SlideOutDownAnimation = keyframes`
+    from {
+      transform: translate3d(0, 0, 0);
+    }
+  
+    to {
+      visibility: hidden;
+      transform: translate3d(0, 100%, 0);
+    }
+  `;
+  
+  //extend BaseAnimation component and create 
+  //your custom styled animation
+  const SlideOutDown = styled(BaseAnimation)`
+    animation-name: ${SlideOutDownAnimation};
+  `;
+   
+  //export your custom styled animation  
+  export default SlideOutDown;
+```
+
+now your animation is a styled-component and you can use this like any other styled-component, 
+passing the all BaseAnimation [props](https://github.com/dielduarte/animate-css-styled-components#props).
+
 # WIP
  - tests with jest
  - `animate` component, wrapper for all animations with a only component.