docs: addtions to client/server section

Mention the unique_filename option in the client/server section and also
note that fio will produce aggregate summary output for all jobs when
running jobs on multiple servers.

Signed-off-by: Vincent Fu <vincent.fu@samsung.com>

HOWTO.rst

@@ -5385,5 +5385,10 @@ containing two hostnames ``h1`` and ``h2`` with IP addresses 192.168.10.120 and
 	/mnt/nfs/fio/192.168.10.120.fileio.tmp
 	/mnt/nfs/fio/192.168.10.121.fileio.tmp
 
+This behavior can be disabled by the :option:`unique_filename` option.
+
 Terse output in client/server mode will differ slightly from what is produced
 when fio is run in stand-alone mode. See the terse output section for details.
+
+Also, if one fio invocation runs workloads on multiple servers, fio will
+provide at the end an aggregate summary report for all workloads.

fio.1

@@ -5142,8 +5142,13 @@ containing two hostnames `h1' and `h2' with IP addresses 192.168.10.120 and
 .PD
 .RE
 .P
+This behavior can be disabled by the \fBunique_filename\fR option.
+.P
 Terse output in client/server mode will differ slightly from what is produced
 when fio is run in stand-alone mode. See the terse output section for details.
+.P
+Also, if one fio invocation runs workloads on multiple servers, fio will
+provide at the end an aggregate summary report for all workloads.
 .SH AUTHORS
 .B fio
 was written by Jens Axboe <axboe@kernel.dk>.