docs: switch to English document (#2426)

Thanks to

- @hotNoder
- @freebyron
- @Azard
- @rccoder
- @cemremengu
- @SunShinewyf
- @lslxdx 
- @zhang-z
- @gztchan
- @DarrenWong
- @freebyron
- @davidnotes

docs/_config.yml

@@ -2,8 +2,8 @@ title: Egg.js
 subtitle: "Born to build better enterprise frameworks and apps"
 description: "Born to build better enterprise frameworks and apps"
 language:
-- zh-cn
 - en
+- zh-cn
 timezone: UTC
 url: https://eggjs.org
 root: /
@@ -26,4 +26,4 @@ less:
 
 deer:
   spmAPos: 'a454'
-  spmBPos: 'b4893'
+  spmBPos: 'b4893'

docs/source/en/intro/quickstart.md

@@ -1,8 +1,6 @@
 title: Quick Start
 ---
 
-# Quick Start
-
 This guide covers getting up and running a real example using Egg.
 By following along with this guide step by step, you can quickly get started with Egg development.