[SPARK-32190][PYTHON][DOCS] Development - Contribution Guide in PySpark

### What changes were proposed in this pull request?

This PR proposes to document PySpark specific contribution guides at "Development" section.

Here is the demo for reviewing quicker: https://hyukjin-spark.readthedocs.io/en/stable/development/contributing.html

### Why are the changes needed?

To have a single place for PySpark users, and better documentation.

### Does this PR introduce _any_ user-facing change?

Yes, it is a new documentation. See the demo linked above.

### How was this patch tested?

```bash
cd docs
SKIP_SCALADOC=1 SKIP_RDOC=1 SKIP_SQLDOC=1 jekyll serve --watch
```

and

```bash
cd python/docs
make clean html
```

Closes #29596 from HyukjinKwon/SPARK-32190.

Authored-by: HyukjinKwon <gurwls223@apache.org>
Signed-off-by: HyukjinKwon <gurwls223@apache.org>

python/docs/source/development/contributing.rst

@@ -0,0 +1,93 @@
+..  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.
+
+=======================
+Contributing to PySpark
+=======================
+
+There are many types of contribution, for example, helping other users, testing releases, reviewing changes,
+documentation contribution, bug reporting, JIRA maintenance, code changes, etc.
+These are documented at `the general guidelines <http://spark.apache.org/contributing.html>`_.
+This page focuses on PySpark and includes additional details specifically for PySpark.
+
+
+Contributing by Testing Releases
+--------------------------------
+
+Before the official release, PySpark release candidates are shared in the `dev@spark.apache.org <http://apache-spark-developers-list.1001551.n3.nabble.com/>`_ mailing list to vote on.
+This release candidates can be easily installed via pip. For example, in case of Spark 3.0.0 RC1, you can install as below:
+
+.. code-block:: bash
+
+    pip install https://dist.apache.org/repos/dist/dev/spark/v3.0.0-rc1-bin/pyspark-3.0.0.tar.gz
+
+The link for release files such as ``https://dist.apache.org/repos/dist/dev/spark/v3.0.0-rc1-bin`` can be found in the vote thread.
+
+Testing and verifying users' existing workloads against release candidates is one of the vital contributions to PySpark.
+It prevents breaking users' existing workloads before the official release.
+When there is an issue such as a regression, correctness problem or performance degradation worth enough to drop the release candidate,
+usually the release candidate is dropped and the community focuses on fixing it to include in the next release candidate.
+
+
+Contributing Documentation Changes
+----------------------------------
+
+The release documentation is located under Spark's `docs <https://github.com/apache/spark/tree/master/docs>`_ directory.
+`README.md <https://github.com/apache/spark/blob/master/docs/README.md>`_ describes the required dependencies and steps
+to generate the documentations. Usually, PySpark documentation is tested with the command below
+under the `docs <https://github.com/apache/spark/tree/master/docs>`_ directory:
+
+.. code-block:: bash
+
+    SKIP_SCALADOC=1 SKIP_RDOC=1 SKIP_SQLDOC=1 jekyll serve --watch
+
+PySpark uses Sphinx to generate its release PySpark documentation. Therefore, if you want to build only PySpark documentation alone,
+you can build under `python/docs <https://github.com/apache/spark/tree/master/python>`_ directory by:
+
+.. code-block:: bash
+
+    make html
+
+It generates the corresponding HTMLs under ``python/docs/build/html``.
+
+Lastly, please make sure that the new APIs are documented by manually adding methods and/or classes at the corresponding RST files
+under ``python/docs/source/reference``. Otherwise, they would not be documented in PySpark documentation.
+
+
+Preparing to Contribute Code Changes
+------------------------------------
+
+Before starting to work on codes in PySpark, it is recommended to read `the general guidelines <http://spark.apache.org/contributing.html>`_.
+There are a couple of additional notes to keep in mind when contributing to codes in PySpark:
+
+* Be Pythonic.
+* APIs are matched with Scala and Java sides in general.
+* PySpark specific APIs can still be considered as long as they are Pythonic and do not conflict with other existent APIs, for example, decorator usage of UDFs.
+
+
+Code Style Guide
+----------------
+
+Please follow the style of the existing codebase as is, which is virtually PEP 8 with one exception: lines can be up
+to 100 characters in length, not 79.
+
+Note that the method and variable names in PySpark are the similar case is ``threading`` library in Python itself where
+the APIs were inspired by Java. PySpark also follows `camelCase` for exposed APIs that match with Scala and Java.
+There is an exception ``functions.py`` that uses `snake_case`. It was in order to make APIs SQL (and Python) friendly.
+
+PySpark leverages linters such as `pycodestyle <https://pycodestyle.pycqa.org/en/latest/>`_ and `flake8 <https://flake8.pycqa.org/en/latest/>`_, which ``dev/lint-python`` runs. Therefore, make sure to run that script to double check.
+

python/docs/source/development/index.rst

@@ -19,3 +19,8 @@
 Development
 ===========
 
+.. toctree::
+    :maxdepth: 2
+
+    contributing
+