README: avahi Troubleshooting: add a NixOS-specific tip.

README.html

@@ -1250,7 +1250,11 @@ <h3 id="avahidns_sd-bonjourzeroconf-issues">1. <strong>Avahi/DNS_SD
 systems may instead use the mdnsd daemon as an alternative to provide
 DNS-SD service. (FreeBSD offers both alternatives, but only Avahi was
 tested; see <a
-href="https://gist.github.com/reidransom/6033227">here</a>.)</p>
+href="https://gist.github.com/reidransom/6033227">here</a>.) A NixOS
+user found that in NixOS, this error can also occur if avahi-daemon
+service IS running with publishing enabled, but reports “the error
+disappeared on NixOS by setting services.avahi.openFirewall to
+true”.</p>
 <ul>
 <li><strong>uxplay starts, but either stalls or stops after “Initialized
 server socket(s)” appears (<em>without the server name showing on the

README.md

@@ -997,6 +997,9 @@ You might need to edit the avahi-daemon.conf file (it is typically in /etc/avahi
 make sure that "disable-publishing" is **not** a selected option).
 Some  systems  may instead use the mdnsd daemon as an alternative to provide DNS-SD service.
 (FreeBSD offers both alternatives, but only Avahi was tested; see [here](https://gist.github.com/reidransom/6033227).)
+A NixOS user found that in NixOS, this error can also occur if avahi-daemon service IS running with publishing enabled,
+but reports "the error disappeared on NixOS by setting services.avahi.openFirewall to true".
+
 
 * **uxplay starts, but either stalls or stops after "Initialized server socket(s)" appears (_without the server name showing on the client_)**.
 

README.txt

@@ -1279,7 +1279,10 @@ start, stop, status. You might need to edit the avahi-daemon.conf file
 "disable-publishing" is **not** a selected option). Some systems may
 instead use the mdnsd daemon as an alternative to provide DNS-SD
 service. (FreeBSD offers both alternatives, but only Avahi was tested;
-see [here](https://gist.github.com/reidransom/6033227).)
+see [here](https://gist.github.com/reidransom/6033227).) A NixOS user
+found that in NixOS, this error can also occur if avahi-daemon service
+IS running with publishing enabled, but reports "the error disappeared
+on NixOS by setting services.avahi.openFirewall to true".
 
 -   **uxplay starts, but either stalls or stops after "Initialized
     server socket(s)" appears (*without the server name showing on the