Adding required /etc/hosts entries to docs/contributing.rst
Adding required /etc/hosts entries to docs/contributing.rst

bsmr-misc-forks/letsencrypt,bsmr-misc-forks/letsencrypt,thanatos/lets-encrypt-preview,wteiken/letsencrypt,brentdax/letsencrypt,thanatos/lets-encrypt-preview,wteiken/letsencrypt,stweil/letsencrypt,mitnk/letsencrypt,dietsche/letsencrypt,stweil/letsencrypt,jtl999/certbot,lmcro/letsencrypt,jtl999/certbot,jsha/letsencrypt,letsencrypt/letsencrypt,lmcro/letsencrypt,letsencrypt/letsencrypt,DavidGarciaCat/letsencrypt,mitnk/letsencrypt,dietsche/letsencrypt,DavidGarciaCat/letsencrypt,brentdax/letsencrypt,jsha/letsencrypt