🎉 add CONTRIBUTING.md

Author: jvdd

CONTRIBUTING.md

@@ -0,0 +1,92 @@
+# Contributing to tsdownsample
+
+Welcome! We're happy to have you here. Thank you in advance for your contribution to tsdownsample.
+
+## The basics
+
+tsdownsample welcomes contributions in the form of Pull Requests. For small changes (e.g., bug fixes), feel free to submit a PR. For larger changes (e.g., new functionality, major refactoring), consider submitting an [Issue](https://github.com/predict-idlab/tsdownsample/issues) outlining your proposed change.
+
+### Prerequisites
+
+tsdownsample is written in Rust. You'll need to install the [Rust toolchain](https://www.rust-lang.org/tools/install) for development.  
+
+This project uses the nightly version of Rust. You can install it with:
+
+```bash
+rustup install nightly
+```
+
+and then set it as the default toolchain with:
+
+```bash
+rustup default nightly
+```
+
+### tsdownsample 
+
+The structure of the tsdownsample project is as follows:
+
+```bash
+tsdownsample
+├── Cargo.toml
+├── README.md
+├── src
+│   ├── lib.rs     # Python bindings for Rust library
+├── tsdownsample   # The Python package
+├── downsample_rs  # Rust library containing the actual implementation
+├── tests          # Tests for the Python package
+```
+
+The Rust library is located in the `downsample_rs` directory. The Python package is located in the `tsdownsample` directory. The `src/lib.rs` file contains the Python bindings for the Rust library.
+
+Under the hood most downsampling algorithms heavily rely on the [argminmax](https://github.com/jvdd/argminmax) - a SIMD accelerated library for finding the index of the minimum and maximum values in an array. If you want to improve the performance of the library, you could also take a look at the `argminmax` library.
+
+### Testing
+
+Changes to the downsample_rs library can be tested with:
+
+```bash
+cd downsample_rs
+cargo test
+```
+
+Changes to the Python package can be tested using the [`Makefile`](Makefile) in the root directory of the project:
+
+*Make sure you have the test dependencies installed:*
+
+```bash
+pip install -r test/requirements.txt          # Install test dependencies
+pip install -r test/requirements-linting.txt  # Install linting dependencies
+```
+
+To run the tests:
+```bash
+make test
+```
+
+To run the tests and linting:
+```bash
+make lint
+```
+
+### Formatting 
+
+We use [black](https://github.com/psf/black) and [isort](https://github.com/PyCQA/isort) to format the Python code.
+
+To format the code, run the following command (more details in the [Makefile](Makefile)):
+```sh
+make format
+```
+
+*(make sure you have the test linting dependencies installed)*
+
+To format the Rust code, run the following command:
+```sh
+cargo fmt
+```
+
+---
+
+## Improving the performance
+
+When a PR is submitted that improves the performance of the library, we would highly appreciate if the PR also includes a (verifiable) benchmark that shows the improvement.