add -rc option to specify startup options file

README.md

@@ -101,7 +101,8 @@ status](https://repology.org/badge/vertical-allrepos/uxplay.svg)](https://repolo
 
 -   Add any UxPlay options you want to use as defaults to a startup file
     `~/.uxplayrc` (see "`man uxplay`" or "`uxplay -h`" for format and
-    other possible locations). In particular, if your system uses
+    other possible locations; the location can also be set with "uxplay -rc _location_"). 
+    In particular, if your system uses
     PipeWire audio or Wayland video systems, you may wish to add "as
     pipewiresink" or "vs waylandsink" as defaults to the file. *(Output
     from terminal commands "ps waux \| grep pulse" or "pactl info" will
@@ -121,7 +122,9 @@ status](https://repology.org/badge/vertical-allrepos/uxplay.svg)](https://repolo
     can be used to control the daemon.   If it is enabled, the daemon will start
     at the user's first login and stop when they no longer have any open sessions. See
     https://www.baeldung.com/linux/systemd-create-user-services for more about
-    systemd user services.  **Note: it is NOT recommended to run UxPlay as a root service.**
+    systemd user services. If more than one user might simultaneously run uxplay this way, they should
+    specify distinct -p and -m options (ports and deviceID) in their startup files.
+    **Note: it is NOT recommended to run UxPlay as a root service.**
 
 -   On Raspberry Pi:  models using hardware h264 video decoding by the
     Broadcom GPU (models 4B and earlier) may require the uxplay option -bt709.
@@ -413,7 +416,8 @@ package](#building-an-installable-rpm-package).
     dns_sd library. OpenSSL is already installed as a System Library.
 
 -   **OpenBSD:** (doas pkg_add) libplist gstreamer1-plugins-base.
-    avahi-libs must also be installed to provide the dns_sd library.
+    avahi-libs must also be installed to provide the dns_sd library;
+    (avahi-main must also be installed).
     OpenSSL is already installed as a System Library.
 
 #### Building an installable RPM package
@@ -498,8 +502,7 @@ repositories for those distributions.
     pulse, v4l2, ...), (+ gstreamer1-vaapi for Intel/AMD graphics).
 
 -   **OpenBSD:** Install gstreamer1-libav, gstreamer-plugins-\*
-    (\* = core, bad, base, good). avahi-main must also be installed for
-    the avahi_daemon rc startup script.
+    (\* = core, bad, base, good).
 
 ### Starting and running UxPlay
 
@@ -995,6 +998,9 @@ Options:
     comments, and ignored. Command line options supersede options in the
     startup file.
 
+**-rc _file_** can also be used to specify the startup file location: this 
+overrides `$UXPLAYRC`, ``~/.uxplayrc``, etc.
+
 **-n server_name** (Default: UxPlay); server_name@\_hostname\_ will be
 the name that appears offering AirPlay services to your iPad, iPhone
 etc, where *hostname* is the name of the server running uxplay. This