contributing edit

Author: slaizet

docs/source/pages/contributing.rst

@@ -43,3 +43,60 @@ bug not currently referenced by an existing issue, or have an idea on
 how to improve a part of 2DECOMP&FFT, please open a new item on the issue
 tracker before opening a pull request.
 
+# Contributing
+
+1. You want to contribute but have no idea how ? Please refer to the [Get started](#get-started) section.
+2. You have identified a bug ? Please refer to the [Bug](#bug) section.
+3. You have improved a part of the code or have developed a new functionality ? Please refer to the [advanced](#advanced-contribution) section.
+
+## Get started
+
+The recommended strategy to contribute is to start with a [discussion](https://github.com/2decomp-fft/2decomp-fft/discussions) or to pick an existing issue.
+To modify or experiment with the code, fork the 2decomp github repository and commit changes in a dedicated branch of your fork.
+When the modification is ready for review, one can open a pull request as described in the [advanced](#advanced-contribution) section below.
+
+## Bug
+
+It appears that you have identified a bug in the 2decomp library.
+If you are not sure this is really a bug in the library, you should go to the [discussions](https://github.com/2decomp-fft/2decomp-fft/discussions) section and open a new discussion.
+Otherwise, follow the steps below.
+
+Firstly, try to reproduce the error with a debug build of the library, a small problem size and a small number of MPI ranks.
+It makes bug-hunting much easier.
+Unfortunately, this is not always possible.
+Please note that for a debug build, the log contains all the environment variables.
+Use it to hunt the bug but think twice before sharing it as it can expose sensitive and personal information.
+At least, please try to reproduce the bug on another machine with another compiler.
+
+Secondly, if you have modified the source code of the 2decomp library, you must reproduce the bug without the modifications in 2decomp.
+The development team can only provide support for sections of code available in the present repository.
+
+Thirdly, you must provide a minimal working example.
+The program using 2decomp and exposing the bug should be relatively small.
+The development team will not provide support if the program exposing the bug is very long.
+The programs available in the examples section are a good starting point for a minimal working example, ideally you could contribute the minimal working example to the existing examples.
+
+At this stage, you probably did your best to simplify the problem at hand.
+Open an issue and select the bug report template.
+Provide a meaningful title, do your best to complete all the sections of the template and provide the version of the compiler, the version of the MPI / FFT library, ...
+If you think you have a fix for the bug, please expose it inside the issue.
+It is recommended to wait for feedback before opening a pull request.
+
+## Advanced contribution
+
+One should read this section before opening a pull request.
+To fix a bug, please open an issue and use the bug report template first.
+To improve a part of the code or develop a new functionality, please open an issue and use the feature request template first.
+If you are not sure about your contribution, open a [discussion](https://github.com/2decomp-fft/2decomp-fft/discussions) first.
+This helps raise awareness of the work and prevents repeated effort from occurring.
+
+The code in a pull-request should be formatted using the `fprettify` program.
+See the code sample in the `scripts` folder.
+
+Pull requests must be focused, small, coherent and have a detailed description.
+The longer the pull request, the harder the review.
+Please empathise with your fellow contributors who are going to spend time reviewing your code.
+
+As long as the pull request is open for discussion and not ready for merging, convert it to draft.
+Whenever it is ready for merging, convert it to a regular pull request.
+Please note that reviewers might push modifications directly to your branch or request changes.