Add NGINX compile warning

nginx.sample.conf

@@ -11,6 +11,8 @@ server {
 	client_max_body_size 100M; # Change this to the max file size you want to allow
 
 	# Uncomment if you are running lolisafe behind CloudFlare.
+	# This requires NGINX compiled from source with:
+	#	--with-http_realip_module
 	#include /path/to/lolisafe/real-ip-from-cf;
 
 	location / {