readme: add more precise description of our annotated dataset

README.md

@@ -14,4 +14,4 @@ The following classes are supported:
 - Initial
 - Other
 
-The model is based on `faster_rcnn_R_50_FPN_3x` and was fine-tuned on own and manually annotated segments from digitized books.
+The model is based on `faster_rcnn_R_50_FPN_3x` and is fine-tuned on 8.027 manually annotated images, resulting in 5.363 annotated segments.