Corrected info how WORDPRESS_CONFIG_EXTRA is put into effect

wordpress/content.md

@@ -21,7 +21,7 @@ The following environment variables are also honored for configuring your WordPr
 -	`-e WORDPRESS_TABLE_PREFIX=...`
 -	`-e WORDPRESS_AUTH_KEY=...`, `-e WORDPRESS_SECURE_AUTH_KEY=...`, `-e WORDPRESS_LOGGED_IN_KEY=...`, `-e WORDPRESS_NONCE_KEY=...`, `-e WORDPRESS_AUTH_SALT=...`, `-e WORDPRESS_SECURE_AUTH_SALT=...`, `-e WORDPRESS_LOGGED_IN_SALT=...`, `-e WORDPRESS_NONCE_SALT=...` (default to unique random SHA1s, but only if other environment variable configuration is provided)
 -	`-e WORDPRESS_DEBUG=1` (defaults to disabled, non-empty value will enable `WP_DEBUG` in `wp-config.php`)
--	`-e WORDPRESS_CONFIG_EXTRA=...` (defaults to nothing, non-empty value will be embedded verbatim inside `wp-config.php` -- especially useful for applying extra configuration values this image does not provide by default such as `WP_ALLOW_MULTISITE`; see [docker-library/wordpress#142](https://github.com/docker-library/wordpress/pull/142) for more details)
+-	`-e WORDPRESS_CONFIG_EXTRA=...` (defaults to nothing, the value will be evaluated by the `eval()` function in `wp-config.php`. This variable is especially useful for applying extra configuration values this image does not provide by default such as `WP_ALLOW_MULTISITE`; see [docker-library/wordpress#142](https://github.com/docker-library/wordpress/pull/142) for more details)
 
 The `WORDPRESS_DB_NAME` needs to already exist on the given MySQL server; it will not be created by the `%%REPO%%` container.