fix the first launch instructions for Arch

[nickgirga]

I fixed the instructions that the start script for Arch print out. The commands that they previously showed (chmod 755 && ./additional.sh) did not work because chmod requires a file at the end:

Usage: chmod [OPTION]... MODE[,MODE]... FILE...
  or:  chmod [OPTION]... OCTAL-MODE FILE...
  or:  chmod [OPTION]... --reference=RFILE FILE...

(source: chmod --help)

Before the changes, simply copying and pasting the commands from the instructions would cause an error:

Copying and pasting the commands with the slightly changed chmod command, it works just fine:

[supersonictw]

@exalab999 Check it