HISTORY.rst is out of date

[SimKennedy]

Hi,
Thank you for the work on this package.
I just wanted to remind you to update the change history..
I've just had to hunt around for a while to fix issues with dependencies which would have been a lot easier with an up to date HISTORY and list of breaking changes.
Thanks
Sim

[sciyoshi]

@SimKennedy I'm going through a similar process right now. From what I can tell, there's two major breaking changes:

• the DocType import has changed to Document
• class Meta has changed to class Django

@safwanrahman it would be great to know if anything else was a breaking change in the v6 update.

[safwanrahman]

Sorry I could not manage time to update HISTORY.rst.
@sciyoshi I think you need to use the register_document decorator to registar a document is missed. other than that, I think its ok!
Can you add them in history and make a PR?