DOC: add contributor docs

Author: lucascolley

docs/contributing.md

@@ -0,0 +1,74 @@
+# Contributing
+
+Contributions are welcome from any "array-consuming" library contributors who
+have found themselves writing private array-agnostic functions in the process of
+converting code to consume the standard!
+
+## How to contribute a function
+
+- Add the implementation of your function to `src/array_api_extra/_funcs.py`.
+  - Ensure that your function includes type annotations and a
+    [numpydoc-style docstring](https://numpydoc.readthedocs.io/en/latest/format.html).
+  - Add your function to `__all__` at the top of the file.
+- Import your function to `src/array_api_extra/__init__.py` and add it to
+  `__all__` there.
+- Add a test class for your function in `tests/test_funcs.py`.
+- [Make a PR!](https://github.com/data-apis/array-api-extra/pulls)
+
+## Development workflow
+
+If you are an experienced contributor to Python packages, feel free to develop
+however you feel comfortable! However, if you would like some guidance,
+development of array-api-extra is made easy with
+[Pixi](https://pixi.sh/latest/):
+
+- [Clone the repository](https://docs.github.com/en/repositories/creating-and-managing-repositories/cloning-a-repository)
+  at <https://github.com/data-apis/array-api-extra>.
+- `cd array-api-extra`.
+- [Install Pixi](https://pixi.sh/latest/#installation).
+- To enter a development environment:
+
+```
+pixi shell -e dev
+```
+
+- To run the tests:
+
+```
+pixi run test
+```
+
+- To build the docs locally:
+
+```
+pixi run docs
+```
+
+- To install a [pre-commit](https://pre-commit.com) hook and run the lint suite:
+
+```
+pixi run lint
+```
+
+- To enter an interactive Python prompt:
+
+```
+pixi run ipython
+```
+
+- To run individual parts of the lint suite separately:
+
+```
+pixi run pre-commit
+pixi run pylint
+pixi run mypy
+```
+
+Alternative environments are available with a subset of the dependencies and
+tasks available in the `dev` environment:
+
+```
+pixi shell -e docs
+pixi shell -e test
+pixi shell -e lint
+```

docs/index.md

@@ -4,6 +4,7 @@
 :maxdepth: 2
 :hidden:
 api-reference.md
+contributing.md
 ```
 
 This is a library housing "array-agnostic" implementations of functions built on