DOC: Move all docs into en/ subdirectory (#1505)

* DOC: Move all docs into en/ subdirectory

PR #1502 is working on adding a Chinese translation to the docs. In
general, I encouraged this (in #1452) as a path towards getting useful
translated content in the game without requiring a massive
refactor/rearchitecting of everything.

To support this, this takes the first step of moving our docs into an
en/ subdirectory, so that other languages can live alongside. No effort
is made at this time to support or select between alternate languages;
this is a pure-rename refactor.

src/Documentation/doc/en/basic/world.md

@@ -0,0 +1,13 @@
+# World
+
+In Bitburner, the world consists of six different cities:
+
+- Sector-12 (this is where you start out)
+- Aevum
+- Ishima
+- New Tokyo
+- Chongqing
+- Volhaven
+
+Each city has its own map and [Factions](factions.md).
+Each city also offers different services such as gyms, universities, hardware stores, and places of work.