Add outlines documentation and link it in User Guide (issue #3484)

docs/index.rst

@@ -42,6 +42,7 @@ You can contribute to `pypdf on GitHub <https://github.com/py-pdf/pypdf>`_.
    user/file-size
    user/pdf-version-support
    user/pdfa-compliance
+   outlines
 
 
 .. toctree::

docs/outlines.rst

@@ -0,0 +1,27 @@
+=========================
+Working with Outlines
+=========================
+
+Outlines (also known as bookmarks) are used to create a clickable table of contents in a PDF.
+
+Reading outlines
+-----------------
+.. code-block:: python
+
+    from pypdf import PdfReader
+
+    reader = PdfReader("example.pdf")
+    outlines = reader.outline
+    for item in outlines:
+        print(item)
+
+Adding outlines
+----------------
+.. code-block:: python
+
+    from pypdf import PdfWriter
+
+    writer = PdfWriter()
+    writer.add_blank_page(width=200, height=200)
+    writer.add_outline_item("My First Page", 0)
+    writer.write("output.pdf")