Added tooltip on merchant account id setting

lib/class.plugify-gform-braintree.php

@@ -679,7 +679,7 @@ public function feed_settings_fields() {
                         'choices'       => $this->merchant_account_choices(),
                         'required'      => false,
                         'default_value' => '',
-                        'tooltip'       => ''
+                        'tooltip'       => esc_html__('By default the payment will be processed by your primary Braintree merchant account.  If you have multiple merchant accounts configured, you can specify which one this form should pay to here.', 'angelleye-gravity-forms-braintree'),
                     ]
                 ],
             ];