Add an explanation of how to avoid headers sent and cookie-based sessions issues

Author: miled

examples/example_01.php

@@ -5,6 +5,19 @@
 * Most other providers work pretty much the same.
 */
 
+/**
+ * Step 0: Start PHP session
+ *
+ * Normally this step is not required as HybridAuth will attempt to start the session for you, however
+ * in some cases it might be better to call session_start() at top of script to avoid cookie-based sessions
+ * issues. 
+ *
+ * See: http://php.net/manual/en/function.session-start.php#refsect1-function.session-start-notes
+ *      http://stackoverflow.com/a/8028987
+ */
+
+session_start();
+
 /**
  * Step 1: Require the Hybridauth Library
  *