docs: about state

Author: linonetwo

demo/tiddlers/Index.tid

@@ -15,4 +15,10 @@ Button2:
 
 <$likeButtonExampleWidget stateTiddler="$:/state/tw-react/readme/like-button" />
 
+State:
+
+{{$:/state/tw-react/readme/like-button}}
+
+Two buttons have shared state [[$:/state/tw-react/readme/like-button]], but not updated when state changed (you can implement this in the `refresh` method), so when you click one, and close this tiddler then reopen it, you will see two buttons have same ''clicked'' state.
+
 [[Readme|$:/plugins/linonetwo/tw-react/readme]]