add links to child docs referenced within readme

[Grammaresque]

Author checklist (Completed by original Author)

• Good fit for the Rocky Linux project? Title and Author Metatags inserted ?
• If applicable, steps and instructions have been tested to work
• Initial self-review to fix basic typos and grammar completed

Rocky Documentation checklist (Completed by Rocky team)

• 1st Pass (Document is good fit for project and author checklist completed)
• 2nd Pass (Technical Review - check for technical correctness)
• 3rd Pass (Detailed Editorial Review and Peer Review)
• Final approval (Final Review)

[sspencerwire]

Looks good!

[github-actions]

Test results for 43ae76a:

Number of broken URLs: 4

URL,RESULT,FILENAME
 https://www.virtualbox.org/,failed,guides/automation/templates-automation-packer-vsphere.md
 http://laurenzkruty.de,failed,guides/contribute/README.md
 http://sauveur.xyz,failed,guides/contribute/README.md
 https://www.virtualbox.org/wiki/Downloads,failed,guides/virtualization/vbox-rocky.md