updated the README

Signed-off-by: Peter Staar <taa@zurich.ibm.com>

README.md

@@ -1,3 +1,54 @@
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-license: apache-2.0
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+---
+license: apache-2.0
+---
+
+# Regression Dataset for [`docling-parse`](https://github.com/docling-project/docling-parse)
+
+This repository contains the reference dataset used as a regression test corpus for
+[`docling-parse`](https://github.com/docling-project/docling-parse).
+
+Its purpose is to make parser and renderer changes safe: when behavior changes in
+[`docling-parse`](https://github.com/docling-project/docling-parse), the test
+suite can compare the current output against the expected artifacts stored in this
+dataset.
+
+## What this dataset is used for
+
+The dataset serves two related parts of the
+[`docling-parse`](https://github.com/docling-project/docling-parse) test suite:
+
+- `parse`: PDF parsing outputs are checked against stored ground-truth structures,
+  extracted content, and document-specific regression fixtures.
+- `renderer`: rendering outputs are checked against stored render instructions,
+  bitmap artifacts, and page images.
+
+Reference test code is included in this repository under
+`_docling_parse/_tests`, in particular:
+
+- `_docling_parse/_tests/test_parse.py`
+- `_docling_parse/_tests/test_renderer.py`
+
+## Repository contents
+
+The dataset is organized into a few main groups:
+
+- `regression/`: source PDF files used for regression coverage.
+- `groundtruth/`: expected parse outputs for selected pages and documents.
+- `groundtruth_renderer/`: expected renderer outputs such as instruction JSON,
+  bitmap metadata, exported bitmap files, and full-page images.
+- `cases/`, `errors/`, `synthetic/`: additional fixtures covering focused edge
+  cases, failure scenarios, and synthetic test inputs.
+
+## Why this exists
+
+PDF parsing and rendering are both sensitive to small implementation changes.
+This dataset helps detect unintended regressions in:
+
+- text extraction
+- layout and geometry
+- annotations, forms, and shapes
+- bitmap extraction
+- page rendering instructions
+
+In short, this repository is the regression baseline for both the `parse` and the
+`renderer` parts of [`docling-parse`](https://github.com/docling-project/docling-parse).