[configs/releng] Update zsh path to match /etc/shells

Signed-off-by: Gerardo Exequiel Pozzi <vmlinuz386@yahoo.com.ar>
releng: Allow specifying a mirror on the kernel command line.

The new mirror= option takes a mirror URL and creates a new mirrorlist.
When setting mirror=auto, the mirror is taken from archiso_http_srv in
order to keep using the mirror selected in the netboot menu.
Merge remote-tracking branch 'upstream/master'

Conflicts:
	configs/releng/root-image/root/customize_root_image.sh
Merge remote-tracking branch 'origin/master'
Modify pacman.conf, README

Added post installation notes to README and other minor changes