chore: Change toggle button text to English.

Add "Click to show/hide English" to home.

public/_includes/_hero-home.jade

@@ -6,5 +6,6 @@ header(class="background-sky")
     .hero-cta
       a(href="/docs/ts/latest/quickstart.html" class="md-raised button button-large button-plain" md-button) 开始吧！
 
-    h2 点击“译文”可显示/隐藏“原文”，点击“原文”可隐藏自身
+    h2 点击“译文”显示/隐藏“原文”
+    h4 Click to show/hide English
 

public/_includes/_main-nav.jade

@@ -16,4 +16,4 @@ md-toolbar(class="main-nav background-regal l-pinned-top l-layer-5",scroll-y-off
       li.l-right <a class="main-nav-button" href="/docs/ts/latest/quickstart.html" md-button>立即开始！</a>
       li.l-right
         a.main-nav-button.md-button(ng-click="appCtrl.toggleSource($event)", href)
-          span {{appCtrl.sourceVisible?'隐藏原文':'显示原文'}}
+          span {{appCtrl.sourceVisible?'Hide English':'Show English'}}