update readme to include walmart search setting in config

Author: ziming

README.md

@@ -27,6 +27,9 @@ return [
     'api_key' => env('SCRAPINGBEE_API_KEY'),
     'base_url' => env('SCRAPINGBEE_BASE_URL', 'https://app.scrapingbee.com/api/v1/'),
     'timeout' => env('SCRAPINGBEE_TIMEOUT', 120),
+    
+    'google_search_base_url' => env('SCRAPINGBEE_GOOGLE_SEARCH_BASE_URL', 'https://app.scrapingbee.com/api/v1/store/google'),
+    'walmart_search_base_url' => env('SCRAPINGBEE_WALMART_SEARCH_BASE_URL', 'https://app.scrapingbee.com/api/v1/walmart/search'),
 ];
 ```