Add a warning about the extreme insecurity of FPM exposed externally

php/variant-fpm.md

@@ -11,3 +11,5 @@ Some potentially helpful resources:
 -	[very detailed article by Pascal Landau](https://www.pascallandau.com/blog/php-php-fpm-and-nginx-on-docker-in-windows-10/)
 -	[Stack Overflow discussion](https://stackoverflow.com/q/29905953/433558)
 -	[Apache httpd Wiki example](https://wiki.apache.org/httpd/PHPFPMWordpress)
+
+**WARNING:** the FastCGI protocol is inherently trusting, and thus *extremely* insecure to expose outside of a private container network -- unless you know *exactly* what you are doing (and are willing to accept the extreme risk), do not use Docker's `--publish` (`-p`) flag with this image variant.