fix advanced configuration docs
fix advanced configuration docs

Summary: fixed an extra `\` in the `module.name_mapper.extension` docs, and fixed indentation throughout so that it is formatted properly.

Reviewed By: samwgoldman

Differential Revision: D3865541

fbshipit-source-id: 431b8431d446cd70616e1b51cb787bbf5cd0454a

fletcherw/flow,mroch/flow,samwgoldman/flow,MichaelDeBoey/flow,chenglou/flow,claudiopro/flow,AgentME/flow,ForbesLindesay/flow,AprilArcus/flow,ForbesLindesay/flow,MichaelDeBoey/flow,popham/flow,claudiopro/flow,TiddoLangerak/flow,JonathanUsername/flow,JonathanUsername/flow,ForbesLindesay/flow,samwgoldman/flow,popham/flow,ForbesLindesay/flow,ForbesLindesay/flow,gabro/flow,fletcherw/flow,jamesgpearce/flow,chenglou/flow,samwgoldman/flow,samwgoldman/flow,fletcherw/flow,jamesgpearce/flow,nmote/flow,TiddoLangerak/flow,AgentME/flow,chenglou/flow,AprilArcus/flow,jgrund/flow,facebook/flow,nmote/flow,jamesgpearce/flow,JonathanUsername/flow,gabro/flow,mroch/flow,AprilArcus/flow,claudiopro/flow,TiddoLangerak/flow,samwgoldman/flow,gabelevi/flow,popham/flow,JonathanUsername/flow,ylu1317/flow,gabro/flow,gabelevi/flow,JonathanUsername/flow,mroch/flow,MichaelDeBoey/flow,jgrund/flow,jgrund/flow,nmote/flow,mroch/flow,popham/flow,popham/flow,samwgoldman/flow,nmote/flow,chenglou/flow,facebook/flow,gabelevi/flow,AprilArcus/flow,TiddoLangerak/flow,jamesgpearce/flow,jamesgpearce/flow,AprilArcus/flow,chenglou/flow,ylu1317/flow,ylu1317/flow,AprilArcus/flow,gabelevi/flow,chenglou/flow,mroch/flow,TiddoLangerak/flow,gabelevi/flow,claudiopro/flow,ForbesLindesay/flow,jamesgpearce/flow,gabelevi/flow,gabelevi/flow,facebook/flow,jgrund/flow,nmote/flow,MichaelDeBoey/flow,facebook/flow,ylu1317/flow,AgentME/flow,jgrund/flow,MichaelDeBoey/flow,facebook/flow,jamesgpearce/flow,gabro/flow,fletcherw/flow,AgentME/flow,facebook/flow,AgentME/flow,mroch/flow,popham/flow,gabro/flow,nmote/flow,popham/flow,ylu1317/flow,gabro/flow,mroch/flow,claudiopro/flow,JonathanUsername/flow,facebook/flow,fletcherw/flow,jgrund/flow,samwgoldman/flow,fletcherw/flow,nmote/flow,JonathanUsername/flow