docs/man/nut-ipmipsu.txt: add errata note about possible troubles when changing OS user accounts [#3193]

Signed-off-by: Jim Klimov <jimklimov+nut@gmail.com>

Author: jimklimov

docs/man/nut-ipmipsu.txt

@@ -105,6 +105,16 @@ Here is an example output for a Dell r610 server:
 KNOWN ISSUES
 ------------
 
+According to the research in https://github.com/networkupstools/nut/issues/3193
+the driver (or technically the libfreeipmi used in it) may have troubles if it
+changes the run-time user account, which NUT drivers usually do when started as
+`root` by init scripts -- by default they drop privileges to the configured
+user account such as `nut`, `ups` or `nobody`.  If your driver fails to start,
+possibly with a segmentation fault reported, try either changing the context
+to the unprivileged user in init scripts (using `su` or `sudo`) or systemd unit
+(using a drop-in file to set `User=...` in `[Service]` section) before starting
+the actual driver program, or try setting `user=root` in its `ups.conf` section.
+
 include::networked_hostnames.txt[]
 
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