Suggest drupal/webform_config_ignore

[andybroomfield]

We updated the readme in #39 to describe how to ignore config.
Webform Config Ignore
is a module that will set this up out the box.
However there are cases where some webform and webform options we don't want to ignore (BHCC prefixes forms / options with bhcc_ to achive this). So we will want a way of applying the same rule we have in config ignore.

In the mean time, maybe we should add this to composer/suggest and the readme?