Allow to always use OCR extracted text

Fixes: #1628

modules/joex/src/main/resources/reference.conf

@@ -298,6 +298,9 @@ Docpell Update Check
     # and images. If the returned text is shorter than the value
     # below, OCR is run afterwards. Then both extracted texts are
     # compared and the longer will be used.
+    #
+    # If you set this to 0 (or a negative value), then the text parts
+    # of a PDF are ignored and OCR is always run and its result used.
     pdf {
       min-text-len = 500
     }