Editing pass nginx-multisite

[sspencerwire]

• read for spelling and clarity
• added a link to the apache document of the same type and also added a
  link to the nginx document in the apache document
• fixed the preferred use of "web server" instead of "webserver"...
  (oddly, the reverse is true for website, which is preferred as the
  single word)
• fixed the apache document's use of multi-site, because "multisite" is
  now preferred
• fixed the title of the apache document to match the nginx document in
  the menu (Apache Multisite)
• fixed a couple of minor typos in the nginx document
• In the Prerequisites section, added admonition hints instead of the
  indented bullet items, as the indented bullets don't add quite enough
  separation from the content above them
• Great document addition to the repository!!

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)