Minor document changes and fixes

[sspencerwire]

• Removed the Atom editor from the README.md because it is officially
  deprecated by the dev.
• Added NvChad in its place
• fixed "trees" to "tree's" for posessive reference in line for
  mirroring_lsyncd.md doc
• also fixed incorrect word in the admonition ("then" should have been
  "the")
• Added an admonition to lxd_server.md dealing with the deprecaton of
  iptables

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)