Update README.md

found it in config file was going to add option
	# Custom
	include /data/nginx/custom/http_top[.]conf;
 
https://github.com/jc21/nginx-proxy-manager/blob/b7b808d98d787b25548265055d9f8621d31b580e/docker/rootfs/etc/nginx/nginx.conf#L72

docs/advanced-config/README.md

@@ -132,6 +132,7 @@ NPM has the ability to include different custom configuration snippets in differ
 You can add your custom configuration snippet files at `/data/nginx/custom` as follow:
 
  - `/data/nginx/custom/root.conf`: Included at the very end of nginx.conf
+ - `/data/nginx/custom/http_top.conf`: Included at the top of the main http block
  - `/data/nginx/custom/http.conf`: Included at the end of the main http block
  - `/data/nginx/custom/stream.conf`: Included at the end of the main stream block
  - `/data/nginx/custom/server_proxy.conf`: Included at the end of every proxy server block