Update README.md

modules/line_descriptor/README.md

-Binary descriptors for lines extracted from an image
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+Binary Descriptors for Line Segments
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+This module shows how to extract line segments from an image by 2 different methods: First segmenting lines with Line Segment Detector LSDDetector and then (or just) using the Binary Descriptor to get the lines and give them a descriptor -- BinaryDescriptor. Finally, we can then match line segments using the BinaryDescriptorMatcher class.