Fix docs site index page (#3868)

page/index.en-us.md

@@ -2,6 +2,7 @@
 date: "2016-11-08T16:00:00+02:00"
 title: "Documentation"
 slug: "documentation"
+url: "/en-us/"
 weight: 10
 toc: true
 draft: false

page/index.fr-fr.md

@@ -2,6 +2,7 @@
 date: "2017-08-23T09:00:00+02:00"
 title: "Documentation"
 slug: "documentation"
+url: "/fr-fr/"
 weight: 10
 toc: true
 draft: false

page/index.zh-cn.md

@@ -2,6 +2,7 @@
 date: "2016-11-08T16:00:00+02:00"
 title: "文档"
 slug: "documentation"
+url: "/zh-cn/"
 weight: 10
 toc: true
 draft: false

page/index.zh-tw.md

@@ -2,6 +2,7 @@
 date: "2016-11-08T16:00:00+02:00"
 title: "文件"
 slug: "documentation"
+url: "/zh-tw/"
 weight: 10
 toc: true
 draft: false