Added comment

config/nginx/common/locations.conf

@@ -9,6 +9,8 @@ location = /favicon.ico {
 }
 
 location = /robots.txt {
+	# Some WordPress plugin gererate robots.txt file
+	# Refer #340 issue
 	try_files $uri $uri/ /index.php?$args;
 	access_log off;
 	log_not_found off;