add instructions on using nmcli

[hbjydev]

This commit adds instructions (tested on a freshly-installed RL8.5 install) for configuring networking using nmcli, in parallel to the network-scripts documentation that currently exists.

Author checklist (Completed by original Author)

• Contribution a good fit for the Rocky project? Title and Author MetaTags inserted ?
• Is this a non-English contribution?
• If applicable, steps and instructions have been tested to work on a real system
• Did you perform an initial self-review to fix basic typos and grammatical correctness

Rocky Documentation checklist (Completed by Rocky team)

• 1st Pass (Check that document is good fit for project and author checklist completed)
• 2nd Pass (Technical Review - check for technical correctness)
• 3rd Pass (Basic Editorial Review)
• 4th Pass (Detailed Editorial Review and Peer Review)
• Final pass/approval (Final Review)

[hbjydev]

Not sure if the order of these two sections wants to swap (i.e. nmcli section on page load, config files on the second tab), I just put it in after the existing stuff.

[hbjydev]

Oh, my bad, looks like docs.rl.org removed the content tabs feature. Need to reformat.