Move zh contents to top level.

The change is because legacy gitbook is not stable and new gitbook.com
is recommended. But the new gitbook doesn't support multi-lang yet. So
only zh is supported now on gitbook publiched site.

en contents would be added later after it is offically supported.

CONTRIBUTING.md

@@ -1,8 +1,7 @@
-# CONTRIBUTING
-
-1. [Fork on Github](https://github.com/feiskyer/kubernetes-handbook/fork).
-2. Clone the forked repo: `git clone https://github.com/<user-name>/kubernetes-handbook -b en`.
-3. Create a new branch, add some changes and commit: `git checkout -b new-branch`.
-4. Push the branch to github: `git commit -am "comments"; git push`.
-5. File a Pull Request on Github to [master](https://github.com/feiskyer/kubernetes-handbook) branch.
+# 如何贡献
 
+1. 在 Github 上 [Fork](https://github.com/feiskyer/kubernetes-handbook/fork) 项目到自己的仓库。
+2. 将 fork 后的项目拉到本地: `git clone https://github.com/<user-name>/kubernetes-handbook`。
+3. 新建一个分支，并添加或编辑内容：`git checkout -b new-branch`。
+4. 提交并推送到 github：`git commit -am "comments"; git push`。
+5. 在 Github 上提交 Pull Request。

book.json

@@ -7,7 +7,7 @@
         "mermaid",
         "github",
         "editlink",
-        "anchor-navigation-ex-toc",
+        "page-toc",
         "-lunr",
         "-search",
         "search-plus",
@@ -19,20 +19,18 @@
         "fontSize": 11
     },
     "pluginsConfig": {
+        "page-toc": {
+          "selector": ".markdown-section h1, .markdown-section h2, .markdown-section h3",
+          "position": "before-first",
+          "showByDefault": true
+        },
         "github": {
             "url": "https://github.com/feiskyer/kubernetes-handbook"
         },
         "editlink": {
-            "base": "https://github.com/feiskyer/kubernetes-handbook/blob/master/",
+            "base": "https://github.com/feiskyer/kubernetes-handbook/blob/master",
             "label": "编辑本页"
         },
-	"anchor-navigation-ex-toc": {
-		"showLevel": false,
-		"mode": "float",
-		"float": {
-			"showLevelIcon": false
-		}
-	},
         "tbfed-pagefooter": {
           "copyright":"&copy Pengfei Ni",
           "modify_label": "Updated at",