Document how to pass custom headers through the DefaultNetworkLayer
Document how to pass custom headers through the DefaultNetworkLayer

Summary: This came up as a question on Stack Overflow[0], so I thought we should
document this.

[0]: http://stackoverflow.com/questions/32550061
Closes https://github.com/facebook/relay/pull/310

Reviewed By: @josephsavona

Differential Revision: D2439371

mcanthony/relay,NevilleS/relay,vjeux/relay,facebook/relay,ide/relay,yungsters/relay,facebook/relay,jshanson7/relay,kassens/relay,iamchenxin/relay,voideanvalue/relay,heracek/relay,apalm/relay,AnSavvides/relay,iamchenxin/relay,facebook/relay,wincent/relay,chirag04/relay,Aweary/relay,cesarandreu/relay,michaelchum/relay,atxwebs/relay,mroch/relay,Aweary/relay,almasakchabayev/relay,kangkot/relay,iamchenxin/relay,venepe/relay,chentsulin/relay,jtthrillson/relay,wangcan2014/relay,cpojer/relay,xuorig/relay,beni55/relay,iamchenxin/relay,benjaminogles/relay,voideanvalue/relay,dbslone/relay,freiksenet/relay,wangcan2014/relay,apalm/relay,Aweary/relay,dmfrancisco/relay,bneiluj/relay,beni55/relay,IlyasM/relayWorking,NevilleS/relay,rosskevin/relay,jshanson7/relay,cesarandreu/relay,dmfrancisco/relay,chentsulin/relay,atxwebs/relay,magnus-lycka/relay,kassens/relay,xuorig/relay,freiksenet/relay,niklasvh/relay,josephsavona/relay,wincent/relay,voideanvalue/relay,IlyasM/relayWorking,andimarek/generic-relay,zpao/relay,xymostech/relay,kangkot/relay,cpojer/relay,mcanthony/relay,xuorig/relay,voideanvalue/relay,zpao/relay,andimarek/generic-relay,tmitchel2/relay,almasakchabayev/relay,niklasvh/relay,wincent/relay,AnSavvides/relay,ide/relay,u9520107/relay,IlyasM/relayWorking,tmitchel2/relay,mcanthony/relay,apalm/relay,vjeux/relay,xuorig/relay,voideanvalue/relay,dbslone/relay,andimarek/generic-relay,facebook/relay,venepe/relay,josephsavona/relay,gabelevi/relay,bneiluj/relay,kassens/relay,heracek/relay,xymostech/relay,xuorig/relay,michaelchum/relay,facebook/relay,cesarandreu/relay,atxwebs/relay,jeffmo/relay,heracek/relay,magnus-lycka/relay,rosskevin/relay,yungsters/relay,facebook/relay,cpojer/relay,kassens/relay,michaelchum/relay,almasakchabayev/relay,niklasvh/relay,kangkot/relay,mroch/relay,u9520107/relay,dmfrancisco/relay,jtthrillson/relay,xymostech/relay,forter/generic-relay,gabelevi/relay,kassens/relay,chirag04/relay,gabelevi/relay,voideanvalue/relay,chentsulin/relay,wincent/relay,benjaminogles/relay,atxwebs/relay,AnSavvides/relay,jeffmo/relay,tmitchel2/relay,jtthrillson/relay,Shopify/relay,wangcan2014/relay,kassens/relay,xuorig/relay,venepe/relay,Shopify/relay,benjaminogles/relay,zpao/relay,vjeux/relay,wincent/relay,chirag04/relay,freiksenet/relay,mroch/relay,beni55/relay,Shopify/relay,u9520107/relay,josephsavona/relay,bneiluj/relay,NevilleS/relay,jeffmo/relay,magnus-lycka/relay,jshanson7/relay,ide/relay,yungsters/relay,cpojer/relay,wincent/relay