docs(subscription): translate source subscription.md<100%>

doc/subscription.md

@@ -1,19 +1,19 @@
-# Subscription
+# Subscription (订阅)
 
-**What is a Subscription?** A Subscription is an object that represents a disposable resource, usually the execution of an Observable. A Subscription has one important method, `unsubscribe`, that takes no argument and just disposes the resource held by the subscription. In previous versions of RxJS, Subscription was called "Disposable".
+**什么是 Subscription ？** - Subscription 是表示可清理资源的对象，通常是 Observable 的执行。Subscription 有一个重要的方法，即 `unsubscribe`，它不需要任何参数，只是用来清理由 Subscription 占用的资源。在上一个版本的 RxJS 中，Subscription 叫做 "Disposable" (可清理对象)。
 
 ```js
 var observable = Rx.Observable.interval(1000);
 var subscription = observable.subscribe(x => console.log(x));
-// Later:
-// This cancels the ongoing Observable execution which
-// was started by calling subscribe with an Observer.
+// 稍后：
+// 这会取消正在进行中的 Observable 执行
+// Observable 执行是通过使用观察者调用 subscribe 方法启动的
 subscription.unsubscribe(); 
 ```
 
-<span class="informal">A Subscription essentially just has an `unsubscribe()` function to release resources or cancel Observable executions.</span>
+<span class="informal"> Subscription 基本上只有一个 `unsubscribe()` 函数，这个函数用来释放资源或去取消 Observable 执行。</span>
 
-Subscriptions can also be put together, so that a call to an `unsubscribe()` of one Subscription may unsubscribe multiple Subscriptions. You can do this by "adding" one subscription into another:
+Subscription 还可以合在一起，这样一个 Subscription 调用 `unsubscribe()` 方法，可能会有多个 Subscription 取消订阅 。你可以通过把一个 Subscription  添加到另一个上面来做这件事：
 
 ```js
 var observable1 = Rx.Observable.interval(400);
@@ -25,12 +25,13 @@ var childSubscription = observable2.subscribe(x => console.log('second: ' + x));
 subscription.add(childSubscription);
 
 setTimeout(() => {
-  // Unsubscribes BOTH subscription and childSubscription
+  // subscription 和 childSubscription 都会取消订阅
   subscription.unsubscribe();
 }, 1000);
 ```
 
-When executed, we see in the console:
+执行时，我们在控制台中看到：
+
 ```none
 second: 0
 first: 0
@@ -39,4 +40,4 @@ first: 1
 second: 2
 ```
 
-Subscriptions also have a `remove(otherSubscription)` method, in order to undo the addition of a child Subscription.
+Subscriptions 还有一个 `remove(otherSubscription)` 方法，用来撤销一个已添加的子 Subscription 。