(maint) Update installation instruction for consistency SSH Runner

[adiati98]

Issue

Closes #484

Procedure

I replaced the shorthand options with their full equivalents and added green highlighting to the environment variables.

Reference
https://docs.drone.io/runner/ssh/installation/

[bradrydzewski]

@tphoney thoughts on which is more clear, the left or the right? I feel like I started using the example on the left because it was more effective to see real-world value and people were confused by the {{variable}} notation but it has been sol long I can't remember.

[MarieReRe]

@bradrydzewski could we perhaps do a mix of the two? highlight the real world example to draw attention without the {{variable}} syntax?

[tphoney]

Hi @adiati98 thanks for bringing this to our attention its tricky to make it intuitive, we spent some time coming up with a better format and i took your change and made some tweaks #493 was merged. (your commit is still merged)

thanks again 🌈