Update BUILDFORAP2.md

BUILDFORAP2.md

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 Experimental Build Instructions for AirPlay 2
 ==
-* This code is experimental and much of the normal functionality of Shairport Sync is broken. Please do not use it in situations where reliable service is expected!
+* This code is experimental and much of the normal functionality of Shairport Sync is broken. Please do not use it in situations where reliable service is expected.
 * Be especially careful with audio systems capable of very high volume output -- the volume control in this software may not be reliable!
 * Initially, at least, leave the settings in the configuration file at default except as noted below.
 * At the time of writing, May 2, 2021, everything is on the latest version of the software -- macOS 11..3, iOS 14.5, Raspberry Pi OS 5.10.17-v7l+ (Buster), Ubuntu 20.04 -- fully updated.
-* AirPlay 2 seems to use a timing system based on the [IEEE-1588 Precision Timing Protocol (PTP)](https://standards.ieee.org/standard/1588-2008.html). Shairport Sync relies on a program called [`nqptp`](https://github.com/mikebrady/nqptp) to monitor PTP signals. This program uses ports 319 and 320 and replaces any PTP service you have on the computer.
+* AirPlay 2 uses a timing system based on the [IEEE-1588 Precision Timing Protocol (PTP)](https://standards.ieee.org/standard/1588-2008.html). Shairport Sync relies on a program called [`nqptp`](https://github.com/mikebrady/nqptp) to monitor PTP signals. This program uses ports 319 and 320 and replaces any PTP service you have on the computer.
   In addition, `nqptp` must run with `root` privileges.  
  (FYI, most computers do not have a PTP clock running -- instead, they may use a [Network Timing Protocol (NTP)](http://www.ntp.org) service to keep the system clock synchronised with world time.)
 * When Shairport Sync is updated, you should check and update `nqptp` *before* building the update.