Added "env" command

Credit: https://github.com/basilfx/kippo-extra

Result: 
```bash
root@nas3:~# env
LOGNAME=root
USER=root
HOME=/root
PATH=/bin:/usr/bin:/sbin:/usr/sbin
_=/usr/bin/env
LANG=en_US.UTF-8
TERM=xterm-256color
SHELL=/bin/bash
LANGUAGE=en_GB:en
SHLVL=1
SSH_TTY=/dev/pts/0
PWD=/root
MAIL=/var/mail/root
root@nas3:~# 
```