Fix spelling mistake in usage.rst
Fix spelling mistake in usage.rst

databae -> database
171767313/django-simple-captcha,jichu4n/flask-captcha,171767313/django-simple-captcha,jichu4n/flask-captcha,mbi/django-simple-captcha,mbi/django-simple-captcha,171767313/django-simple-captcha,mbi/django-simple-captcha