Added options attribute addition documentation
Added options attribute addition documentation

I was tasked to create a product that would be out-of-the-box available to our users, so I added the attributes in a data migration but I had a hard time finding any resource that describes adding options via code and had to dig through Oscar's code on GitHub to figure this out. People would benefit from an addition like this, at least save time from digging through code to figure this out.
michaelkuty/django-oscar,itbabu/django-oscar,sonofatailor/django-oscar,john-parton/django-oscar,django-oscar/django-oscar,solarissmoke/django-oscar,sasha0/django-oscar,WillisXChen/django-oscar,okfish/django-oscar,itbabu/django-oscar,spartonia/django-oscar,solarissmoke/django-oscar,eddiep1101/django-oscar,okfish/django-oscar,WillisXChen/django-oscar,sonofatailor/django-oscar,ka7eh/django-oscar,john-parton/django-oscar,michaelkuty/django-oscar,taedori81/django-oscar,spartonia/django-oscar,WillisXChen/django-oscar,django-oscar/django-oscar,anentropic/django-oscar,itbabu/django-oscar,michaelkuty/django-oscar,sasha0/django-oscar,eddiep1101/django-oscar,django-oscar/django-oscar,WillisXChen/django-oscar,anentropic/django-oscar,WillisXChen/django-oscar,okfish/django-oscar,ka7eh/django-oscar,anentropic/django-oscar,itbabu/django-oscar,ka7eh/django-oscar,sasha0/django-oscar,sonofatailor/django-oscar,WillisXChen/django-oscar,solarissmoke/django-oscar,solarissmoke/django-oscar,okfish/django-oscar,john-parton/django-oscar,sasha0/django-oscar,anentropic/django-oscar,michaelkuty/django-oscar,taedori81/django-oscar,eddiep1101/django-oscar,spartonia/django-oscar,taedori81/django-oscar,sonofatailor/django-oscar,eddiep1101/django-oscar,spartonia/django-oscar,ka7eh/django-oscar,taedori81/django-oscar,john-parton/django-oscar,django-oscar/django-oscar