Append register form with customer address

[dbrmn]

Hi fellow devs!

We're trying to append the customer register-form with address-fields, but the docs has led us in circles...

- In the file `templates/customers/register.liquid` we have a `create_customer`-form.

- With, for example a zip code field, we have tried adding inputs with:

• `name="customer[default_address][zip]"`
• `name="customer[addresses][0][zip]"`
• `name="customer_address[zip]"`

but none of this is stored on submit. 

The goal is to register a new customer AND store address fields on the same post-req.

Anyone experiencing similar issues? Any thoughts would be helpful!