[PR] Redirect /docs/ to /en/docs/
[PR] Redirect /docs/ to /en/docs/

Summary:
Fixes #3602

Not sure this is the way to go, and I can't really test it since it's at the S3 level, but maybe samwgoldman can tell whether it's correct.
Closes https://github.com/facebook/flow/pull/3607

Differential Revision: D4795171

Pulled By: gabelevi

fbshipit-source-id: 00e0ad86cb6b4861bd3d9d6f671b544d90d288d3

fletcherw/flow,TiddoLangerak/flow,nmote/flow,popham/flow,AgentME/flow,samwgoldman/flow,nmote/flow,facebook/flow,jamesgpearce/flow,mroch/flow,fletcherw/flow,JonathanUsername/flow,fletcherw/flow,gabelevi/flow,JonathanUsername/flow,mroch/flow,JonathanUsername/flow,ylu1317/flow,samwgoldman/flow,TiddoLangerak/flow,jamesgpearce/flow,nmote/flow,facebook/flow,jamesgpearce/flow,JonathanUsername/flow,MichaelDeBoey/flow,MichaelDeBoey/flow,claudiopro/flow,claudiopro/flow,gabelevi/flow,samwgoldman/flow,JonathanUsername/flow,MichaelDeBoey/flow,JonathanUsername/flow,mroch/flow,jamesgpearce/flow,gabelevi/flow,claudiopro/flow,popham/flow,TiddoLangerak/flow,AgentME/flow,popham/flow,TiddoLangerak/flow,AgentME/flow,samwgoldman/flow,mroch/flow,ylu1317/flow,facebook/flow,gabelevi/flow,ylu1317/flow,popham/flow,fletcherw/flow,claudiopro/flow,nmote/flow,mroch/flow,popham/flow,claudiopro/flow,gabelevi/flow,TiddoLangerak/flow,nmote/flow,ylu1317/flow,mroch/flow,AgentME/flow,JonathanUsername/flow,jamesgpearce/flow,facebook/flow,samwgoldman/flow,MichaelDeBoey/flow,nmote/flow,nmote/flow,fletcherw/flow,jamesgpearce/flow,samwgoldman/flow,facebook/flow,popham/flow,facebook/flow,facebook/flow,MichaelDeBoey/flow,gabelevi/flow,samwgoldman/flow,gabelevi/flow,fletcherw/flow,ylu1317/flow,mroch/flow,jamesgpearce/flow,popham/flow,AgentME/flow