Add a CSV to OPML example.

examples/csv-to-opml.csv

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+Text,Url
+Example,https://example.org
+Another Example,https://example.org/another

examples/csv-to-opml.py

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+import csv
+
+from opyml import OPML, Outline
+
+
+def main() -> None:
+    document = OPML()
+
+    with open("examples/csv-to-opml.csv", "r") as example_csv:
+        csv_reader = csv.DictReader(example_csv)
+
+        for row in csv_reader:
+            document.body.outlines.append(
+                Outline(
+                    # Convert to str because text is a required OPML attribute
+                    # and row.get() can return None.
+                    text=str(row.get("Text")),
+                    xml_url=row.get("Url"),
+                )
+            )
+
+    print(document.to_xml())
+
+
+if __name__ == "__main__":
+    main()