Better build option for rootfs.tar.

CMD /bin/sh is just always a better default option
Removed git from installation, just install cURL

Due to the debilitating bugs with installing git, I've decided to pull
all git installation for now and just focus on cURL to get something
working out there.
Symlinked files no longer used in busybox.

`/etc/resolv.conf` and `/sbin/init` are no longer symlinks in busybox builds
so we no longer need to overwrite them to get them to work with docker.
Updated README.md: removed git, cleaned up.
Cleaned up run.sh for cURL only image.
New rootfs.tar and md5 file for cURL only image.