Update README.md

Author: gaearon

README.md

@@ -267,3 +267,29 @@ Redux has no opinion on how you do this in your project.
 I wrote a lot of vanilla Flux code, and my only use case for it was avoiding emitting a change before a related Store consumes the action. In Redux this doesn't matter because the change is only emitted after *all* Stores have consumed the action.
 
 If several of your Stores want to read data from each other and depend on each other, it's a sign they should've been a single Store instead. [See this discussion on how `waitFor` can be replaced by the composition of stateless Stores.](https://gist.github.com/gaearon/d77ca812015c0356654f)
+
+### My views aren't updating!
+
+Redux makes a hard assumption that you never mutate the state passed to you. It's easy! For example, instead of
+
+```js
+function (state, action) {
+  state.isAuthenticated = true;
+  state.email = action.email;
+  return state;
+}
+```
+
+you should write
+
+```js
+function (state, action) {
+  return {
+    ...state,
+    isAuthenticated: true,
+    email: action.email
+  };
+}
+```
+
+[Read more](https://github.com/sebmarkbage/ecmascript-rest-spread) about the spread properties ES7 proposal.