Add info to main status help page.

Fixes #728.

web/plates/status-help.html

@@ -11,4 +11,4 @@
     </ul>
     <p class="text-warning">Devices must be manually enabled on the <strong>Settings</strong> page.</p>
 
-    <p>Additional statistics include the number of detected software-defined radios (SDRs), number of current DHCP network clients, uptime, temperature of the Raspberry Pi CPU, and the current clock settings on both the Raspberry Pi, and the total amount of available space on the micro SD card.</p>
+    <p>Additional statistics include the number of detected software-defined radios (SDRs), number of current DHCP network clients, uptime, temperature of the Raspberry Pi CPU (normal range 0°C to 70°C), and the total amount of available space on the micro SD card (normal range >100 MiB).</p>