Clarify non-x86 hardware info sources for snmpd (librenms#12253)

* Clarify non-x86 hardware info sources for snmpd

* Clarify that ARM platforms use device tree, not SMBIOS _(maybe consider a wrapper script for this too?)_
* Non-GPS based systems can also provide lat & lon, such as Galileo or Beidou
* Clarify that Distro means Distribution

* Update SNMP-Configuration-Examples.md

Author: dorkmatt

doc/Support/SNMP-Configuration-Examples.md

@@ -380,6 +380,13 @@ is mode 0400. One solution is to include `@reboot chmod 444
 /sys/devices/virtual/dmi/id/product_serial` in the crontab for root or
 equivalent.
 
+Non-x86 or SMBIOS-based systems, such as ARM-based Raspberry Pi units should
+query device tree locations for this metadata, for example:
+```
+extend hardware '/bin/cat /sys/firmware/devicetree/base/model'
+extend serial '/bin/cat /sys/firmware/devicetree/base/serial-number'
+```
+
 The LibreNMS server include a copy of this example here:
 
 ```

snmpd.conf.example

@@ -5,12 +5,18 @@ group MyROGroup v2c        readonly
 view all    included  .1                               80
 access MyROGroup ""      any       noauth    exact  all    none   none
 
-syslocation Rack, Room, Building, City, Country [GPSX,Y]
+syslocation Rack, Room, Building, City, Country [Lat, Lon]
 syscontact Your Name <[email protected]>
 
-#Distro Detection
+#OS Distribution Detection
 extend distro /usr/bin/distro
-#Hardware Detection (uncomment to enable)
-#extend hardware '/bin/cat /sys/devices/virtual/dmi/id/product_name'
+
+#Hardware Detection
+# (uncomment for x86 platforms)
 #extend manufacturer '/bin/cat /sys/devices/virtual/dmi/id/sys_vendor'
+#extend hardware '/bin/cat /sys/devices/virtual/dmi/id/product_name'
 #extend serial '/bin/cat /sys/devices/virtual/dmi/id/product_serial'
+
+# (uncomment for ARM platforms)
+#extend hardware '/bin/cat /sys/firmware/devicetree/base/model'
+#extend serial '/bin/cat /sys/firmware/devicetree/base/serial-number'