Updated KISS Extended API (markdown)

KISS-Extended-API.md

@@ -22,5 +22,10 @@ Payloads for commands are sent and expected as big endian and defined as:
   // KISS command 8
   struct RebootModem {
   } __attribute__((packed));
+
+  // KISS command 9
+  struct Telemetry {
+    int16_t batteryVoltage;
+  } __attribute__((packed));
 `
 ```