Add details on proper rendering of repeated form type

[weaverryan]

A note should be added to clarify the proper rendering of the error, since you typically render the two underlying fields, but the error is on the parent field:

{{ form_errors(form.password) }}

{{ form_label(form.password.first) }}
{{ form_widget(form.password.first) }}

{{ form_label(form.password.second) }}
{{ form_widget(form.password.second) }}

[weaverryan]

This issue is still valid. I think it would be great to include this in the repeated type form reference document itself, under the Example Usage.