Update README.md

Author: klutchell

docs/advanced-config/README.md

@@ -24,6 +24,7 @@ You can add your custom configuration snippet files at `/data/nginx/custom` as f
 
  - `/data/nginx/custom/root.conf`: Included at the very end of nginx.conf
  - `/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
  - `/data/nginx/custom/server_redirect.conf`: Included at the end of every redirection server block
  - `/data/nginx/custom/server_stream.conf`: Included at the end of every stream server block