📝 sbb_textline_detector: Document OCR-D Usage

README.md

@@ -18,7 +18,14 @@ sudo pip install .
 sbb_textline_detector -i 'image file name' -o 'directory to write output xml' -m 'directory of models'
 
 
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+## Usage with OCR-D
+~~~
+ocrd-example-binarize -I OCR-D-IMG -O OCR-D-IMG-BIN
+ocrd_sbb_textline_detector -I OCR-D-IMG-BIN -O OCR-D-SEG-LINE-SBB -p '{ "model": "/path/to/the/models/textline_detection" }'
+~~~
+
+Segmentation works on raw RGB images, but respects and retains
+`AlternativeImage`s from binarization steps, so it's a good idea to do
+binarization first, then perform the textline detection. The used binarization
+processor must produce an `AlternativeImage` for the binarized image, not
+replace the original raw RGB image.