Update comments in vncserver configuration file example

Issue

• Update the Quick HowTo in comments to be consistent with RHEL documentation.

  $ more /lib/systemd/system/vncserver@.service
  # The vncserver service unit file
  #
  # Quick HowTo:
  # 1. Copy this file to /etc/systemd/system/vncserver@.service
  # 2. Edit <USER> and vncserver parameters appropriately
  #   ("runuser -l <USER> -c /usr/bin/vncserver %i -arg1 -arg2")
  # 3. Run `systemctl daemon-reload`
  # 4. Run `systemctl enable vncserver@:<display>.service`
  

In step 2. of comment section, actually 2 lines need to be modified instead of just the first line("runuser -l <USER> -c /usr/bin/vncserver %i -arg1 -arg2")

It should be

ExecStart=/sbin/runuser -l USER -c "/usr/bin/vncserver %i -geometry 1280x1024"
PIDFile=/home/USER/.vnc/%H%i.pid