Fix typo in README
Fix typo in README

Ref: https://github.com/lqez/django-summernote/issues/25
dhirajt/django-summernote,lqez/django-summernote,rizumu/django-summernote,rizumu/django-summernote,dhirajt/django-summernote,dhirajt/django-summernote,WQuanfeng/django-summernote,summernote/django-summernote,lqez/django-summernote,summernote/django-summernote,summernote/django-summernote,un33k/django-summernote,lqez/django-summernote,WQuanfeng/django-summernote,un33k/django-summernote,WQuanfeng/django-summernote,rizumu/django-summernote,un33k/django-summernote