SSH Auth docs improvement

[k0dard]

Changes

Some small changes in the ssh auth part of the docs:

• Some commands concerning generating ssh keys were misleading (cat is used for viewing files and not generating ssh keys)
• Added formatting for ssh-privatekey and known-hosts keys
• Added instructions on how to get known-hosts value for GitHub

Submitter Checklist

As the author of this PR, please check off the items in this checklist:

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Release Notes

NONE

[linux-foundation-easycla]

• ✅login: k0dard / (b3a20af)
• ✅login: k0dard / (b3a20af, ebd6d6a)
• ✅login: k0dard / (b3a20af, ebd6d6a, be409f9)

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[k0dard]

/kind documentation