docs: update chunking usage docs, minor reorg (#550)

Signed-off-by: Panos Vagenas <35837085+vagenas@users.noreply.github.com>

docs/reference/docling_document.md

@@ -0,0 +1,52 @@
+# Docling Document
+
+This is an automatic generated API reference of the DoclingDocument type.
+
+::: docling_core.types.doc
+    handler: python
+    options:
+        members:
+            - DoclingDocument
+            - DocumentOrigin
+            - DocItem
+            - DocItemLabel
+            - ProvenanceItem
+            - GroupItem
+            - GroupLabel
+            - NodeItem
+            - PageItem
+            - FloatingItem
+            - TextItem
+            - TableItem
+            - TableCell
+            - TableData
+            - TableCellLabel
+            - KeyValueItem
+            - SectionHeaderItem
+            - PictureItem
+            - ImageRef
+            - PictureClassificationClass
+            - PictureClassificationData
+            - RefItem
+            - BoundingBox
+            - CoordOrigin
+            - ImageRefMode
+            - Size
+        show_if_no_docstring: true
+        show_submodules: true
+        docstring_section_style: list
+        filters: ["!^_"]
+        heading_level: 2
+        show_root_toc_entry: true
+        inherited_members: true
+        merge_init_into_class: true
+        separate_signature: true
+        show_root_heading: true
+        show_root_full_path: false
+        show_signature_annotations: true
+        show_source: false
+        show_symbol_type_heading: true
+        show_symbol_type_toc: true
+        show_labels: false
+        signature_crossrefs: true
+        summary: true