Add support for appear and appear-active classes

docs/10.1-animation.md

@@ -85,6 +85,7 @@ You'll notice that when you try to remove an item `ReactCSSTransitionGroup` keep
 ```
 
 ### Custom Classes ###
+
 It is also possible to use custom class names for each of the steps in your transitions. Instead of passing a string into transitionName you can pass an object containing either the `enter` and `leave` class names, or an object containing the `enter`, `enter-active`, `leave-active`, and `leave` class names. If only the enter and leave classes are provided, the enter-active and leave-active classes will be determined by appending '-active' to the end of the class name. Here are two examples using custom classes:
 
 ```javascript
@@ -94,7 +95,9 @@ It is also possible to use custom class names for each of the steps in your tran
       enter: 'enter',
       enterActive: 'enterActive',
       leave: 'leave',
-      leaveActive: 'leaveActive'
+      leaveActive: 'leaveActive',
+      appear: 'appear',
+      appearActive: 'appearActive'
     }>
     {item}
   </ReactCSSTransitionGroup>
@@ -102,7 +105,8 @@ It is also possible to use custom class names for each of the steps in your tran
   <ReactCSSTransitionGroup
     transitionName={
       enter: 'enter',
-      leave: 'leave'
+      leave: 'leave',
+      appear: 'appear'
     }>
     {item2}
   </ReactCSSTransitionGroup>