Distinguish user guide from agent reference in module docstring

The docstring pointed readers at SKILL.md as a "comprehensive guide," but
SKILL.md is written in a dense, skill-oriented format for agents — humans
are better served by the online user guide. Put the online docs first as
the primary reference and label the SKILL.md link as the agent reference.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: timsaucer

python/datafusion/__init__.py

@@ -48,12 +48,11 @@
 >>> result.to_pydict()
 {'grand_total': [16]}
 
-For a comprehensive guide to the DataFrame API -- including a SQL-to-DataFrame
-reference table, expression building, idiomatic patterns, and common pitfalls --
-see ``SKILL.md`` at the root of the datafusion-python repository:
-https://github.com/apache/datafusion-python/blob/main/SKILL.md
+User guide and full documentation: https://datafusion.apache.org/python
 
-Full documentation: https://datafusion.apache.org/python
+AI agent reference (SQL-to-DataFrame mappings, expression-building patterns,
+common pitfalls), written in a dense, skill-oriented format:
+https://github.com/apache/datafusion-python/blob/main/SKILL.md
 """
 
 from __future__ import annotations