🚧 ppn2ocr: Update README

README.md

@@ -58,11 +58,14 @@ firefox OCR-D-OCR-CALAMARI-EVAL/OCR-D-OCR-CALAMARI-EVAL_00000024.html
 
 ppn2ocr
 -------
-The `ppn2ocr` script produces OCR output for a given document in the State
+The `ppn2ocr` script produces a METS file with the best images for a given
-Library Berlin (SBB)'s digitized collection. The document must be specified by its
+document in the State Library Berlin (SBB)'s digitized collection. The document
-PPN, for example:
+must be specified by its PPN, for example:
 ~~~
-./ppn2ocr PPN77164308X
+pip install -r requirements-ppn2ocr.txt
+~/devel/my_ocrd_workflow/ppn2ocr PPN77164308X
+cd PPN77164308X
+~/devel/my_ocrd_workflow/run-docker-hub -I BEST --skip-validation
 ~~~
 
 This produces a workspace directory `PPN77164308X` with the OCR results in it;