Document that manual ISO build needs a HTTP proxy
Originally created by @muri on #11046 (Redmine)
as mention in https://mailman.boum.org/pipermail/tails-dev/2016-February/010174.html, live build does not work without setting a http proxy (it fails in config/chroot_local-hooks/10-tbb when trying to curl the tbb package). i used
lb config —apt-http-proxy http://localhost:3142
in my case, thats on a jessie system with live-build from tails (Tails:6.0/builder-wheezy)