Added disk form_factor meta label

The requirement from field engineers is knowledge of the form factor of the device, i.e. 3.5", 2.5"

* updated EXAMPLE.md
* fixed copy-paste issue `Starting systemd_exporter`

Signed-off-by: Konstantin Shalygin <k0ste@k0ste.ru>

main.go

@@ -91,7 +91,7 @@ func main() {
 	kingpin.Parse()
 	logger := promlog.New(promlogConfig)
 
-	level.Info(logger).Log("msg", "Starting systemd_exporter", "version", version.Info())
+	level.Info(logger).Log("msg", "Starting smartctl_exporter", "version", version.Info())
 	level.Info(logger).Log("msg", "Build context", "build_context", version.BuildContext())
 
 	devices := *smartctlDevices

metrics.go

@@ -43,6 +43,7 @@ var (
 			"firmware_version",
 			"ata_version",
 			"sata_version",
+			"form_factor",
 		},
 		nil,
 	)

smartctl.go

@@ -109,6 +109,7 @@ func (smart *SMARTctl) mineDevice() {
 		smart.json.Get("firmware_version").String(),
 		smart.json.Get("ata_version.string").String(),
 		smart.json.Get("sata_version.string").String(),
+		smart.json.Get("form_factor.name").String(),
 	)
 }