Document how to run simulators as systemd services

Change-Id: I9405d7f36ecbe742b3402fd09dfa38b9e37121a7
Task: 12050
Story: 1751571

doc/source/admin/index.rst

@@ -0,0 +1,31 @@
+
+Configuring simulators
+======================
+
+Running simulators in background
+--------------------------------
+
+The simulators run as interactive processes attached to the
+terminal by default. You can create a systemd service to run the
+emulators in background.
+For each emulator create a systemd unit file and
+update full path to ``sushy-static`` or ``sushy-emulator`` binary and
+adjust arguments as necessary, for example::
+
+  [Unit]
+  Description=Sushy Libvirt emulator
+  After=syslog.target
+
+  [Service]
+  Type=simple
+  ExecStart=/<full-path>/sushy-emulator --port 8000 --libvirt-uri "qemu:///system"
+  StandardOutput=syslog
+  StandardError=syslog
+
+If you want to run simulators with different configuration, for example,
+``sushy-static`` simulator with different mockup files, then create a new
+systemd unit file.
+
+You can also use ``gunicorn`` to run ``sushy-emulator``, for example::
+
+  ExecStart=/usr/bin/gunicorn sushy_tools.emulator.main:app

doc/source/index.rst

@@ -8,6 +8,7 @@ Documentation
   :maxdepth: 2
 
   install/index
+  admin/index
   user/index
   contributor/index