Fixed a couple of minor issues in firewalld.md

[sspencerwire]

• sudo user as an option for root user
• fixed typo in postgresql service addition line

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 ddf97e0:

Number of broken URLs: 0

URL,RESULT,FILENAME