docs: php configuration guide

docs/config.md

@@ -90,7 +90,7 @@ other.example.com {
 ...
 ```
 
-Using the `php_server` directive is generaly what you need,
+Using the `php_server` directive is generally what you need,
 but if you need full control, you can use the lower level `php` directive:
 
 Using the `php_server` directive is equivalent to this configuration:
@@ -139,6 +139,11 @@ Unlike with FPM and CLI SAPIs, environment variables are **not** exposed by defa
 
 To propagate environment variables to `$_SERVER` and `$_ENV`, set the `php.ini` `variables_order` directive to `EGPCS`.
 
+## PHP config
+
+To load [additional *.ini](https://www.php.net/manual/en/configuration.file.php#configuration.file.scan) files the
+environment variable `PHP_INI_SCAN_DIR` is used. PHP will search and include all *.ini files in the given folder.
+
 ## Enable the Debug Mode
 
 When using the Docker image, set the `CADDY_GLOBAL_OPTIONS` environment variable to `debug` to enable the debug mode: