docs: convert ai-coding-assistants page from markdown to rst, shorten title

Every other page in `docs/source/user-guide` and the top-level
`docs/source` is written in reStructuredText; the lone `.md` page was
an inconsistency. Rewrite in rst so the ASF header matches the rest of
the tree, cross-references can use `:py:func:` roles if we ever add
any, and myst is no longer required just to render this one page.

Also shorten the page title from "Using DataFusion with AI Coding
Assistants" to "Using AI Coding Assistants" -- it already sits under
the DataFusion user guide so the product name is redundant.

Verified with `sphinx-build -W --keep-going`.

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

Author: timsaucer

docs/source/ai-coding-assistants.md

@@ -0,0 +1,82 @@
+.. Licensed to the Apache Software Foundation (ASF) under one
+.. or more contributor license agreements.  See the NOTICE file
+.. distributed with this work for additional information
+.. regarding copyright ownership.  The ASF licenses this file
+.. to you under the Apache License, Version 2.0 (the
+.. "License"); you may not use this file except in compliance
+.. with the License.  You may obtain a copy of the License at
+
+..   http://www.apache.org/licenses/LICENSE-2.0
+
+.. Unless required by applicable law or agreed to in writing,
+.. software distributed under the License is distributed on an
+.. "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+.. KIND, either express or implied.  See the License for the
+.. specific language governing permissions and limitations
+.. under the License.
+
+Using AI Coding Assistants
+==========================
+
+If you write DataFusion Python code with an AI coding assistant, this
+project ships machine-readable guidance so the assistant produces
+idiomatic code rather than guessing from its training data.
+
+What is published
+-----------------
+
+- `SKILL.md <https://github.com/apache/datafusion-python/blob/main/SKILL.md>`_ —
+  a dense, skill-oriented reference covering imports, data loading,
+  DataFrame operations, expression building, SQL-to-DataFrame mappings,
+  idiomatic patterns, and common pitfalls. Follows the
+  `Agent Skills <https://agentskills.io>`_ open standard.
+- `llms.txt <llms.txt>`_ — an entry point for LLM-based tools following the
+  `llmstxt.org <https://llmstxt.org>`_ convention. Categorized links to the
+  skill, user guide, API reference, and examples.
+
+Both files live at stable URLs so an agent can discover them without a
+checkout of the repo.
+
+Installing the skill
+--------------------
+
+**Preferred:** run
+
+.. code-block:: shell
+
+    npx skills add apache/datafusion-python
+
+This installs the skill in any supported agent on your machine (Claude
+Code, Cursor, Windsurf, Cline, Codex, Copilot, Gemini CLI, and others).
+The command writes the pointer into the agent's configuration so that any
+project you open that uses DataFusion Python picks up the skill
+automatically.
+
+**Manual:** if you are not using the ``skills`` registry, paste this
+single line into your project's ``AGENTS.md`` or ``CLAUDE.md``::
+
+    For DataFusion Python code, see https://github.com/apache/datafusion-python/blob/main/SKILL.md
+
+Most assistants resolve that pointer the first time they see a
+DataFusion-related prompt in the project.
+
+What the skill covers
+---------------------
+
+Writing DataFusion Python code has a handful of conventions that are easy
+for a model to miss — bitwise ``&`` / ``|`` / ``~`` instead of Python
+``and`` / ``or`` / ``not``, the lazy-DataFrame immutability model, how
+window functions replace SQL correlated subqueries, the ``case`` /
+``when`` builder syntax, and the ``in_list`` / ``array_position`` options
+for membership tests. The skill enumerates each of these with short,
+copyable examples.
+
+It is *not* a replacement for this user guide. Think of it as a distilled
+reference the assistant keeps open while it writes code for you.
+
+If you are an agent author
+--------------------------
+
+The skill file and ``llms.txt`` are the two supported integration
+points. Both are versioned along with the release and follow open
+standards — no project-specific handshake is required.