Remove User Account of Pi

It is wise to make pi account disabled.

1) Add new user 'adduser'
2) Check current group 'pi' is included by 'groups pi'
3) Add new user to the groups above 'sudo adduser (new) (group)'
4) Kill all pi processes --- by default, Xserver is running so change setting from 'raspi-config'
5) Delete pi --- 'sudo deluser pi'

Setting up headless pi - ssh and wifi

Now it becomes quite easy to set up headless setting.
touch ssh in /boot mounted in FAT file system and
write wpa_supplicant.conf in that path as well.

No need to edit Linux file system any more.