Discovered a URL error

[sspencerwire]

• documents were referencing the "Contribute" section, but were returning 404 because no index.md existed
• this is a simple introduction to the contribute section to fix this reference issue.

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)

[github-actions]

Test results for bcae595:

Number of broken URLs: 7

URL,RESULT,FILENAME
 https://docs.rockylinux.org/guides/contribute/,failed,rocky_insights/blogs/index.md
 https://dotfyle.com/,failed,books/nvchad/plugins/index.md
 https://www.stigviewer.com/stig/red_hat_enterprise_linux_8/,failed,books/disa_stig/disa_stig_part1.md
 https://www.stigviewer.com/stig/web_server/,failed,books/disa_stig/disa_stig_part3.md
 http://$(hostname):8080,failed,guides/repositories/pulp_fetch_upload.md
 https://docs.rockylinux.org/guides/contribute/,failed,guides/contribute/style_guide.md
 https://kojidev.rockylinux.org/koji/builds?state=3&order=-build_id,failed,guides/package_management/package_dev_start.md