README: remove notes about unmerged pull request of django-threadedcomments
README: remove notes about unmerged pull request of django-threadedcomments

This feature is merged in, so django-threadedcomments can be utilized now.

PetrDlouhy/django-fluent-comments,Afnarel/django-fluent-comments,edoburu/django-fluent-comments,PetrDlouhy/django-fluent-comments,django-fluent/django-fluent-comments,BangorUniversity/django-fluent-comments,mgpyh/django-fluent-comments,edoburu/django-fluent-comments,mgpyh/django-fluent-comments,django-fluent/django-fluent-comments,BangorUniversity/django-fluent-comments,PetrDlouhy/django-fluent-comments,akszydelko/django-fluent-comments,mgpyh/django-fluent-comments,django-fluent/django-fluent-comments,Afnarel/django-fluent-comments,akszydelko/django-fluent-comments,edoburu/django-fluent-comments,Afnarel/django-fluent-comments,django-fluent/django-fluent-comments,BangorUniversity/django-fluent-comments,akszydelko/django-fluent-comments