Added examples, tweaked print job

examples/print.php

@@ -0,0 +1,17 @@
+<?php
+
+require_once __DIR__."/../vendor/autoload.php";
+
+use NoccyLabs\Lpr\PrintJob;
+
+$job = new PrintJob("image.png");
+
+// Configure
+$job->setPrinter("QL-570");
+$job->setMedia("A4");
+
+// Additional options can be set like this
+$job->setOption("fit-to-page", true);
+
+// Invoke lpr to print the image
+$job->submit();

examples/simple.php

@@ -0,0 +1,13 @@
+<?php
+
+require_once __DIR__."/../vendor/autoload.php";
+
+use NoccyLabs\Lpr\PrintJob;
+
+$job = new PrintJob("image.png");
+
+// Configure
+$job->setPrinter("PDF");
+
+// Invoke lpr to print the image
+$job->submit();

src/PrintJob.php

@@ -94,6 +94,12 @@ class PrintJob
      */
     public function submit()
     {
+        if (!file_exists($this->document)) {
+            throw new LprException(
+                sprintf("The document could not be printed because the file could not be found: %s", $this->document)
+            );
+        }
+
         $options = [];
         if ($this->server !== null) {
             $options[] = "-H";