Update systemd generate script, since no intermediate startup script

[jeevatkm]

aah intermediate startup scripts removed to bring same experience on single and non-single binary as part #178.

This requires update on systemd service file generation command

aah g s -n systemd -i github.com/user/appname

• [x] Implementation
• [x] Documentation update

[jeevatkm]

Documentation update is done 😄