ci/README: basic instructions for running locally

These should be extended upon by someone more knowledgeable with the
topic, but that's the basic information I would want to find there
in order to start debugging CI issues locally.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/3681>

diff --git a/ci/README.txt b/ci/README.txt
index d8ca328..37dfc69 100644 (file)
--- a/ci/README.txt
+++ b/ci/README.txt
@@ -7,3 +7,36 @@ Continuous Integration system.
 * Docker images
 
 * Build scripts and code
+
+Basic instructions for reproducing CI issues locally
+====================================================
+
+Note the URL of the image in the job logs, for instance:
+
+```
+Using docker image sha256:ac097589af0f486321adf7e512f2237c55533b9b08dabb49164a521a374d406d for registry.freedesktop.org/ocrete/gstreamer/amd64/fedora:2022-12-10.0-main with digest registry.freedesktop.org/ocrete/gstreamer/amd64/fedora@sha256:a2f7be944964a115ada2b3675c190bc9a094a5b35eba64a1ac38d52d55d13663
+```
+
+Pull the image:
+
+```
+docker pull registry.freedesktop.org/ocrete/gstreamer/amd64/fedora:2022-12-10.0-main
+```
+
+Run it:
+
+```
+docker run -it fedora:2022-12-10.0-main
+```
+
+At this point, you want to clone the relevant branch, eg if the issue occurs with main:
+
+```
+git clone https://gitlab.freedesktop.org/gstreamer/gstreamer.git
+cd gstreamer
+```
+
+Adapt the above to your situation.
+
+Now, export the relevant variables by observing the job logs and `.gitlab-ci.yml` at
+he root of the GStreamer repository, then run the steps listed in the script section.