added readme and config example

config example might missing config examples... ?! :D

README.md

@@ -0,0 +1,7 @@
+## build
+```bash
+apt install libmosquitto-dev
+cp config.h.example config.h
+# edit config.h
+make
+```

config.h.example

@@ -0,0 +1,2 @@
+#define MQTT_USER1 "<user>"
+#define MQTT_PASS "<pass>"