Document Fedora packaging

Signed-off-by: Cristian Le <[email protected]>

.github/CONTRIBUTING.md

@@ -1,3 +1,24 @@
+<!-- TOC -->
+
+- [Setting up for development](#setting-up-for-development)
+  - [Quick development](#quick-development)
+  - [Setting up a development environment manually](#setting-up-a-development-environment-manually)
+  - [Post setup](#post-setup)
+  - [Testing](#testing)
+  - [Quick local running](#quick-local-running)
+  - [Building docs](#building-docs)
+  - [Pre-commit](#pre-commit)
+- [Design info](#design-info)
+  - [Basic CMake usage](#basic-cmake-usage)
+  - [File API](#file-api)
+  - [Configuration](#configuration)
+  - [Builders](#builders)
+    - [PEP 517 builder](#pep-517-builder)
+    - [Setuptools builder](#setuptools-builder)
+- [Downstream packaging](#downstream-packaging)
+  - [Fedora packaging](#fedora-packaging)
+  <!-- TOC -->
+
 # Setting up for development
 
 See the [Scikit-HEP Developer introduction][skhep-dev-intro] for a detailed
@@ -287,3 +308,34 @@ cmake_extensions=[CMakeExtension("cmake_example")],
 ```
 
 Which should eventually support multiple extensions.
+
+# Downstream packaging
+
+## Fedora packaging
+
+We are using [`packit`](https://packit.dev/) primarily to keep the downstream
+`dist-git` repo at
+[src.fedoraproject.org/rpms/python-scikit-build-core](https://src.fedoraproject.org/rpms/python-scikit-build-core/)
+up to date. There are two `packit` jobs one needs to keep in mind here:
+
+- `copr_build`: Tests the latest commits to `main` as well as any PRs
+- `propose_downstream`: Submits a PR to `src.fedoraproject.org` once a release
+  is published
+
+To interact with `packit`, you can use
+[`/packit command`](https://packit.dev/docs/guide/#how-to-re-trigger-packit-actions-in-your-pull-request)
+in PRs and commit messages or using
+[`packit` CLI](https://packit.dev/docs/cli/). These interactions are primarily
+intended for controlling the CI managed on `scikit-build`.
+
+To debug and build manually we also support
+[`tito`](https://github.com/rpm-software-management/tito) workflow, e.g. to
+build a `srpm` of the latest commit of `scikit-build-core`:
+
+```console
+$ tito build --srpm --test
+```
+
+Both of these methods automatically edit the `Version` in the
+[spec file](../python-scikit-build-core.spec), therefore it is intentionally
+marked as `0.0.0` there to avoid manually updating.