add stripe explanation

booking.admin.inc

@@ -184,7 +184,11 @@ function booking_admin() {
 		'#collapsible' => TRUE, 
 		'#collapsed' => TRUE,    
   );
-
+  $explanation_text = t('<p>Register an account at stripe.com and visit <a href="https://dashboard.stripe.com/account/apikeys">the API keys page</a>, then copy your API keys here.</p>');
+  $form['stripe']['explanation-text'] = array(
+    '#type' => 'container',
+    '#children' => $explanation_text,
+  );      
   $form['stripe']['booking_stripe_test_secret_key'] = array (
     '#type' => 'textfield',
     '#title' => t('Specify Stripe Test Secret Key'),