Add credit to https://github.com/BertrandBordage for initial work

opentech/stream_forms/blocks.py

+# Credit to https://github.com/BertrandBordage for initial implementation
 from django import forms
 from django.db.models import BLANK_CHOICE_DASH
 from django.utils.dateparse import parse_datetime

opentech/stream_forms/models.py

+# Credit to https://github.com/BertrandBordage for initial implementation
 from collections import OrderedDict
 
 from wagtail.wagtailforms.models import AbstractForm