add example of API usage

Signed-off-by: Michael Kaufmann <d00p@froxlor.org>

doc/example/list_functions.php

@@ -0,0 +1,22 @@
+<?php
+
+// include FroxlorAPI helper class
+require __DIR__ . '/FroxlorAPI.php';
+
+// create object of FroxlorAPI with URL, apikey and apisecret
+$fapi = new FroxlorAPI('https://froxlor.your-host.tld/api.php', 'your-api-key', 'your-api-secret');
+
+// send request
+$fapi->request('Froxlor.listFunctions');
+
+// check for error
+if (! empty($fapi->getLastError())) {
+	echo "Error: " . $fapi->getLastError();
+	exit();
+}
+
+// get response of request
+$request = $fapi->getLastResponse();
+
+// view response data
+var_dump($request);