Add mailgun settings to staging

SciPost_v1/settings/staging_do1.py

@@ -36,3 +36,7 @@ WSGI_APPLICATION = 'SciPost_v1.wsgi_staging_do1.application'
 #MONGO_DATABASE['user'] = get_secret('MONGO_DB_USER')
 #MONGO_DATABASE['password'] = get_secret('MONGO_DB_PASSWORD')
 #MONGO_DATABASE['port'] = get_secret('MONGO_DB_PORT')
+
+# Mailgun credentials
+MAILGUN_DOMAIN_NAME = get_secret('MAILGUN_DOMAIN_NAME')
+MAILGUN_API_KEY = get_secret('MAILGUN_API_KEY')