Add note about displaying custom errors.
Add note about displaying custom errors.

jeffkreeftmeijer/phoenix_guides,rafbgarcia/phoenix,trarbr/phoenix,mobileoverlord/phoenix,jwarwick/phoenix,phoenixframework/phoenix,stevedomin/phoenix,0x00evil/phoenix,clessg/phoenix_guides,Joe-noh/phoenix,korobkov/phoenix,rafbgarcia/phoenix,rafbgarcia/phoenix,keathley/phoenix,mobileoverlord/phoenix,gjaldon/phoenix,nshafer/phoenix,mitchellhenke/phoenix,mitchellhenke/phoenix,korobkov/phoenix,evax/phoenix,fblecha/phoenix_guides,larrylv/phoenix_guides,wsmoak/phoenix_guides,bratsche/phoenix_guides,bsmr-erlang/phoenix,mschae/phoenix,mschae/phoenix,Gazler/phoenix,pap/phoenix,optikfluffel/phoenix,stevedomin/phoenix,tianyi33/phoenix_guides,optikfluffel/phoenix,eksperimental/phoenix,oldfartdeveloper/phoenix_guides,Kosmas/phoenix,keathley/phoenix,Joe-noh/phoenix,0x00evil/phoenix,jwarwick/phoenix,phoenixframework/phoenix,dmarkow/phoenix,trarbr/phoenix,dmarkow/phoenix,michalmuskala/phoenix,pap/phoenix,Gazler/phoenix,0x00evil/phoenix,gjaldon/phoenix,tokafish/phoenix_guides,bsmr-erlang/phoenix,3quarterstack/phoenix_guides,nshafer/phoenix,iguberman/phoenix_guides,optikfluffel/phoenix,Kosmas/phoenix,pap/phoenix-guides,thetamind/phoenix_guides,1ternal/phoenix_guides,evax/phoenix,phoenixframework/phoenix,eksperimental/phoenix,michalmuskala/phoenix,nshafer/phoenix