document php-mysql dependency

Signed-off-by: kiara <kiara@bij1.org>

README.md

@@ -4,7 +4,7 @@ This script automates installing Wordpress with all specific BIJ1 plugins,
 template and Advanced Custom Fields settings.
 
 Steps:
-- install `php`
+- install `php` and `php-mysql`
 - First you have to setup a database, e.g. for MariaDB/MySQL (substituting `$WORDPRESS_DB_USER`, `$db`, `$password`):
   - ```sql
     CREATE USER '$WORDPRESS_DB_USER'@'localhost' IDENTIFIED BY '$password';