doc: Add some documentation on generating CI docker images

doc/ci.md

@@ -0,0 +1,30 @@
+# Continuous Integration
+
+Our CI runs on the `gitlab.freedesktop.org` infrastructure. Steps can be found
+in the top-level `gitlab-ci.yml` file.
+
+The current build happens on an x86_64, Fedora 31 image. This should be
+extended to other distrubtions and architectures over time.
+
+## fd.o Registry
+
+The Docker image used for the build process comes from the
+`registry.freedesktop.org` container registry. Images are currently manually
+generate and pushed using the top-level `Dockerfile` and the following steps.
+The assumption is that you are using `podman` as a `docker` alternative. The
+corresponding `docker` command should be easy to find.
+
+```sh
+$ cd <pipewire-top-level-direcory>
+
+# Build the image
+$ podman build --format=docker -t registry.freedesktop.org/pipewire/pipewire/fedora:31 .
+
+# This is usually only needed once. You will be prompted for your fd.o
+# username, and the password is a personal access token that you must generate
+# in the gitlab.fd.o user settings.
+$ podman login
+
+# Upload the image
+$ podman push registry.freedesktop.org/pipewire/pipewire/fedora:31
+```