Improve the readme for the multiple GitHub runners

[Fatme]

This PR improves the GH multiple runners readme.md

• Add the missing step for installing orka CLI
• Reorder the required flags to be prior to the optional
• Remove not needed whitespaces

[svetlimladenov]

I noticed a typo in the self-hosted-runner-manually.md file - here - Sinngle -> Single

[Fatme]

@svetlimladenov

Fixed the Sinngle typo.