Add instructions to readme on how to load fixtures

unisportomat/quiz/fixtures/users.json

+[{"model": "auth.user", "pk": 1, "fields": {"password": "pbkdf2_sha256$260000$75I180x9FwfD0xuW3TGMU4$B1mg2ywC0kSYkbkmFuSyCq8/yxD9nnU7TNq7VmJsnFs=", "last_login": "2021-06-06T07:41:10.617Z", "is_superuser": true, "username": "admin", "first_name": "", "last_name": "", "email": "", "is_staff": true, "is_active": true, "date_joined": "2021-06-05T15:02:57.005Z", "groups": [], "user_permissions": []}}]
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