Add composer autoload guard

bin/orbit

@@ -1,7 +1,30 @@
 #!/usr/bin/env php
 <?php
 
-require_once dirname(__DIR__) . "/vendor/autoload.php";
+// Find where the composer autoload is
+// This tool was installed as a composed dependency or directly
+$root = realpath(dirname(__DIR__));
+$autoload_locations = array(
+    __DIR__ . '/../../../autoload.php',
+    $root . DIRECTORY_SEPARATOR . 'vendor/autoload.php'
+);
+foreach ($autoload_locations as $file) {
+    if (file_exists($file)) {
+        define('ORBIT_COMPOSER_AUTOLOAD', $file);
+        break;
+    }
+}
+
+// Composer autoload require guard
+if (!defined('ORBIT_COMPOSER_AUTOLOAD')) {
+    die(
+        "You must run the command `composer install` from the terminal "
+        . "in the directory '$root' before using this tool.\n"
+    );
+}
+
+// Load composer autoloader
+$autoload = require_once ORBIT_COMPOSER_AUTOLOAD;
 
 // Define command line args for this client
 // And fetch args passed in by invocation