SIFT专利到期了，所以SIFT算法直接在cv2.SIFT_create()中就能实现，代码也应该需要更新了

“以上是 SIFT 算法的总结。关于更多详细信息和理解，强烈建议阅读原始论文。记住一件事，这个算法受到专利保护，所以这个算法被包含在 [opencv contrib repo](https://github.com/opencv/opencv_contrib) 中。”

Locate the documentation containing the quoted SIFT passage and references to the opencv_contrib repository. Check how the current text describes cv2.SIFT_create(); done means the documentation accurately reflects SIFT's availability and no longer presents the patent status as a reason for using contrib.

Written by the indexing model from the issue text.