Enhancement in the documentation

[tvanesse]

I think it's worth mentioning that for old-style classes the order in which we declare the multiple inheritance on the ModelAdmin is important.

More specifically, writing

class MyModelAdmin(admin.ModelAdmin, DjangoObjectActions):
     # your ModelAdmin

won't work because of the depth-first, left-to-right rule whereas

class MyModelAdmin(DjangoObjectActions, admin.ModelAdmin):
     # your ModelAdmin

will work as expected.

So just one sentence in the README might save some time for those trying to use django-object-actions.

By the way thanks a lot for this application, it's really handy.

[crccheck]

The class MyModelAdmin(DjangoObjectActions, admin.ModelAdmin): is already in the README. I want to lean towards keeping the README as small as possible:

1. adding more to the README would increase technical debt
2. I don't have a documentation site yet, so all the usage is crammed into the README right now
3. To keep the README smaller, I aim the README at an intermediate or advanced Python developer. I like the idea of adding a disclaimer to that effect to the top of the README