improve description of behaviour in README

clarify:
- what levels are re-ordered (`ReadingOrder` unaffected/unrelated)
- textual consistency is only the trigger, not the driver
- coordinate-based order respects annotation

README.md

@@ -1,10 +1,12 @@
 # ocrd_repair_inconsistencies
 
-Automatically fix PAGE-XML order inconsistencies in regions, lines and words.
-Children elements are only reordered if reordering by coordinates
-top-to-bottom/left-to-right fixes the appropriately concatenated `TextEquiv`
-texts of the children to match the parent's `TextEquiv` text. This processor
-does not change reading order, just the order of the XML elements in the file.
+Automatically re-order lines, words and glyphs to become textually consistent with their parents.
+
+PAGE-XML elements with textual annotation are re-ordered by their centroid coordinates
+in top-to-bottom/left-to-right fashion iff such re-ordering fixes the inconsistency
+between their appropriately concatenated `TextEquiv` texts with their parent's `TextEquiv` text.
+
+This processor does not affect `ReadingOrder` between regions, just the order of the XML elements below the region level, and only if not contradicting the annotated `textLineOrder`/`readingDirection`.
 
 We wrote this as a one-shot script to fix some files. Use with caution.