`UID` and `GID` args can now be set during build,
so following the example command in the README should fix
[#2](https://tangled.sh/@tangled.sh/knot-docker/issues/2)
by providing a `UID` and `GID` that exist on the host
so that the directories owned by git in the container
can be bind mounted on the host.

I couldn't push or pull from any repositories
until I set `-git-dir` following the instructions in
[knot-hosting](https://tangled.sh/@tangled.sh/core/blob/master/docs/knot-hosting.md#repositories),
so this adds the `/etc/ssh/sshd_config.d/authorized_keys_command.conf` file to `rootfs`.

Not the most elegent solution, but it works™ and should be fine in a
container

bash is now necessary to run the knot post-receive hooks; see
https://tangled.sh/@tangled.sh/core/blob/master/hook/setup.go#L134

Otherwise gives an error of `invalid port specification: "133342"`

Signed-off-by: Anirudh Oppiliappan <anirudh@tangled.sh>