Task

Doc how to add new custom fields to the Submit Event form.
Example of usage with all the types of fields we can add into it.
Example of Doc
http://docs.easydigitaldownloads.com/article/1003-custom-checkout-fields

Maybe even a plugin ( ? )
http://docs.easydigitaldownloads.com/article/1219-checkout-fields-manager-field-types
https://easydigitaldownloads.com/downloads/checkout-fields-manager/