Missing `sudo` on `useradd` and `su - invidious` command in `installation.md`

[Fijxu]

Most of the guide already assumes we are running with a user with sudo privileges due to the commands above. Making a new user requires root privileges and logging into the invidious account also requires root privileges.

documentation/docs/installation.md

Lines 189 to 190 in 4902ecd

	useradd -m invidious
	su - invidious

Issue so I can remember it later