Move content/ into new contentDir content/en/

in preparation for adding new translations such as Chinese.

Paths for "readfile" shortcode are adjusted accordingly.

See #461

content/en/documentation.md

@@ -0,0 +1,20 @@
+---
+title: Hugo Documentation
+linktitle: Hugo
+description: Hugo is the world's fastest static website engine. It's written in Go (aka Golang) and developed by bep, spf13 and friends.
+date: 2017-02-01
+publishdate: 2017-02-01
+menu:
+  main:
+    parent: "section name"
+    weight: 01
+weight: 01	#rem
+draft: false
+slug:
+aliases: []
+toc: false
+layout: documentation-home
+---
+Hugo is the **world's fastest static website engine.** It's written in Go (aka Golang) and developed by [bep](https://github.com/bep), [spf13](https://github.com/spf13) and [friends](https://github.com/gohugoio/hugo/graphs/contributors). 
+
+Below you will find some of the most common and helpful pages from our documentation.