Update MySQL configuration docs to be more accurate

mysql/content.md

@@ -64,7 +64,7 @@ $ docker logs some-%%REPO%%
 
 ## Using a custom MySQL configuration file
 
-The MySQL startup configuration is specified in the file `/etc/mysql/my.cnf`, and that file in turn includes any files found in the `/etc/mysql/conf.d` directory that end with `.cnf`. Settings in files in this directory will augment and/or override settings in `/etc/mysql/my.cnf`. If you want to use a customized MySQL configuration, you can create your alternative configuration file in a directory on the host machine and then mount that directory location as `/etc/mysql/conf.d` inside the `%%IMAGE%%` container.
+The default configuration for MySQL can be found in `/etc/mysql/my.cnf`, which may `!includedir` additional directories such as `/etc/mysql/conf.d` or `/etc/mysql/mysql.conf.d`. Please inspect the relevant files and directories within the `%%IMAGE%%` image itself for more details.
 
 If `/my/custom/config-file.cnf` is the path and name of your custom configuration file, you can start your `%%IMAGE%%` container like this (note that only the directory path of the custom config file is used in this command):