### What changes were proposed in this pull request?
This PR adds few lines about docstring style to document that PySpark follows [NumPy documentation style](https://numpydoc.readthedocs.io/en/latest/format.html). We all completed the migration to NumPy documentation style at SPARK-32085.
Ideally we should have a page like https://pandas.pydata.org/docs/development/contributing_docstring.html but I would like to leave it as a future work.
### Why are the changes needed?
To tell developers that PySpark now follows NumPy documentation style.
### Does this PR introduce _any_ user-facing change?
No, it's a change in unreleased branches yet.
### How was this patch tested?
Manually tested via `make clean html` under `python/docs`:
Closes#30622 from HyukjinKwon/SPARK-33256.
Authored-by: HyukjinKwon <gurwls223@apache.org>
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>
### What changes were proposed in this pull request?
Add type hints guidelines to developer docs.
### Why are the changes needed?
Since it is a new and still somewhat evolving feature, we should provided clear guidelines for potential contributors.
### Does this PR introduce _any_ user-facing change?
No.
### How was this patch tested?
Closes#30094 from zero323/SPARK-33003.
Authored-by: zero323 <mszymkiewicz@gmail.com>
Signed-off-by: HyukjinKwon <gurwls223@apache.org>
### 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>
