Add contributing document.

CONTRIBUTING.md

@@ -0,0 +1,47 @@
+# Contributing to this project
+
+First of all, thank you for wanting to contribute.
+
+## How to submit bug reports or feature requests
+Bug reports or feature requests can be submitted by opening an issue on
+<https://github.com/INCATools/odkcore/issues> or
+<https://github.com/INCATools/ontology-development-kit/issues> (but
+please favour the former, as the latter should now be reserved for
+issues with the Docker images). They may also be sent by e-mail to
+<devel@incenp.org>. When using e-mail, please prefix the subject with
+`[odk ]`.
+
+## How to submit contributions
+Please discuss the change you wish to make first, either through an
+issue or by e-mail (see above), before submitting anything.
+
+Contributions can only be submitted by opening a pull request on
+<https://github.com/INCATools/odkcore/pulls>. Any contribution sent by e-mail
+is likely to be ignored, unless it is a very trivial patch.
+
+Please check your contribution meets the following requirements:
+
+* Python code should pass:
+    * the code quality check (`ruff check`);
+    * the code formatting check (`ruff format --check`);
+    * the static typing check (`mypy`);
+    * the spell check (`codespell`);
+    * and the Python test suite (`pytest tests`).
+* Your patches or commits (when submitting pull requests) should each be
+  adequately described by a [meaningful commit
+  message](https://incenp.org/dvlpt/docs/vcs-good-practices/index.html#sect.commit-messages).
+
+You _may_ additionally ensure that the seed tests also pass (`cd tests && sh
+test-configs.sh`), but this is optional – those tests can take quite a while to
+run, so you are _not_ required to run them locally prior to submitting your
+contribution as they will be run on the pull request anyway.
+
+## About “generative AI”
+Contributions of any kind (code, documentation, tests…) that have been
+fully or partially made by genAI tools are discouraged and will be taken
+as an admission from you that you are perfectly fine with the
+environmental, social, economical, and political external costs
+associated with such tools.
+
+Bug reports or feature requests openly or obviously written by genAI
+tools are equally discouraged and may be ignored.

pyproject.toml

@@ -42,6 +42,7 @@ build-backend = "uv_build"
 module-name = "incatools.odk"
 source-include = [
     "NEWS",
+    "CONTRIBUTING.md",
     "examples/**",
     "tests/**",
 ]