DOC: move OS prereqs out of "advanced configuration"

[mcg1969]

Thank you for the great work, and in advance for your consideration!

Environmental Info:
K3s Version:

k3s version v1.28.3+k3s1 (49411e70)
go version go1.20.10

Node(s) CPU architecture, OS, and Version:

Linux mgrant.sb.anacondaconnect.com 4.18.0-477.27.1.el8_8.x86_64 #1 SMP Thu Aug 31 10:29:22 EDT 2023 x86_64 x86_64 x86_64 GNU/Linux

Describe the bug:
As the documentation says, nm-cloud-setup must be disabled for installation to proceed. I didn't see this, and therefore struggled to understand why the service would not start. I inspected the startup commands, and found the reference to nm-cloud-setup, and that led me to the conclusion it should be deleted.

"Well, problem solved, RTFM, right?" Indeed. And yet. I would like to suggest that installation prerequisites should not go into a section called Advanced Options / Configuration. I was just trying to do some quick and dirty testing, with nothing "advanced" on my mind! It would therefore not occur to me to read anything in a section with Advanced in the title. There is nothing to suggest I'd need to do this in the Quick Start Guide, nor in the Requirements section.

I would like to suggest the following:

• A blurb that links to Requirements at the top of the Quick Start Guide. No matter how quick you want to be, you need to meet the requirements, right?
• A clear callout in said Requirements to common OS-specific requirements such as this. Perhaps is entire section should be moved out of Advanced Options / Configuration and into Requirements.
• I'd consider copying the nm-cloud-setup check in the systemctl script into the get.k3s.io install script as well, perhaps along with checks for ufw and firewalld.

EDIT: Oh, one more add: I discovered the SELinux enforcement with the default k3s-selinux ruleset is not compatible with local-path-provisoner; that should probably be called out as well. See here: rancher/local-path-provisioner#362

Thank you again!

[mcg1969]

I'm not above doing this work myself, mind you—if I get some down time I'll consider doing a doc PR.

[mcg1969]

Closing in favor of k3s-io/docs#195