Add service file

Add the service file to run the buttons application and
install it from the CMakeLists.txt file.

It is not a templated service because the code is hardcoded
to use the instance 0 D-Bus object paths.

Change-Id: I4c57d9f47000bca4a5b1cd445f5bd4a7dfeb8b74
Signed-off-by: Matt Spinler <spinler@us.ibm.com>
diff --git a/service_files/xyz.openbmc_project.Chassis.Buttons.service b/service_files/xyz.openbmc_project.Chassis.Buttons.service
new file mode 100644
index 0000000..f05c00e
--- /dev/null
+++ b/service_files/xyz.openbmc_project.Chassis.Buttons.service
@@ -0,0 +1,13 @@
+[Unit]
+Description=Phosphor Buttons
+
+[Service]
+Restart=always
+RestartSec=3
+ExecStart=/usr/sbin/buttons
+SyslogIdentifier=buttons
+Type=dbus
+BusName=xyz.openbmc_project.Chassis.Buttons
+
+[Install]
+WantedBy=obmc-standby.target