FAQ: env vars for SSL root certs and DNS resolver
FAQ: env vars for SSL root certs and DNS resolver

Added section to FAQ about environment variables, which allow to control
location of SSL root certificate as well as DNS resolver used.

see also comment in #683

yonjah/rclone,ncw/rclone,seuffert/rclone,olihey/rclone,B4dM4n/rclone,yonjah/rclone,ncw/rclone,seuffert/rclone,seuffert/rclone,yonjah/rclone,B4dM4n/rclone,olihey/rclone,ncw/rclone,seuffert/rclone,ncw/rclone,B4dM4n/rclone,olihey/rclone,B4dM4n/rclone,yonjah/rclone,olihey/rclone