Merge pull request reduxjs#1191 from jmrog/store-unsubscribe-documentation

Adds documentation about unsubscribing store listeners to Store.md

Author: gaearon

docs/basics/Store.md

@@ -7,7 +7,8 @@ The **Store** is the object that brings them together. The store has the followi
 * Holds application state;
 * Allows access to state via [`getState()`](../api/Store.md#getState);
 * Allows state to be updated via [`dispatch(action)`](../api/Store.md#dispatch);
-* Registers listeners via [`subscribe(listener)`](../api/Store.md#subscribe).
+* Registers listeners via [`subscribe(listener)`](../api/Store.md#subscribe);
+* Handles unregistering of listeners via the function returned by [`subscribe(listener)`](../api/Store.md#subscribe).
 
 It’s important to note that you’ll only have a single store in a Redux application. When you want to split your data handling logic, you’ll use [reducer composition](Reducers.md#splitting-reducers) instead of many stores.
 
@@ -36,6 +37,7 @@ import { addTodo, completeTodo, setVisibilityFilter, VisibilityFilters } from '.
 console.log(store.getState())
 
 // Every time the state changes, log it
+// (Note that `store.subscribe` returns a function for unregistering the listener)
 let unsubscribe = store.subscribe(() =>
   console.log(store.getState())
 )