Updated Modem control using KISS protocol extension (markdown)

Modem-control-using-KISS-protocol-extension.md

@@ -32,4 +32,9 @@ Payloads for commands are sent and expected as big endian and defined as:
   // KISS command 8
   struct Reboot {
   } __attribute__((packed));
+
+  // KISS command 9
+  struct Telemetry {
+    int16_t batteryVoltage;
+  } __attribute__((packed));
 ```