[glib: 1/3] ci: Improve Docker building instructions slightly

[Simon McVittie <smcv src gnome org>]

commit 8ae795ccba164924f0b09baf4fc00ffbc6be1c06
Author: Philip Withnall <withnall endlessm com>
Date:   Thu Oct 31 10:35:02 2019 +0000

    ci: Improve Docker building instructions slightly
    
    Signed-off-by: Philip Withnall <withnall endlessm com>

 .gitlab-ci/README.md | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)
---
diff --git a/.gitlab-ci/README.md b/.gitlab-ci/README.md
index dc6c82131..6c128796e 100644
--- a/.gitlab-ci/README.md
+++ b/.gitlab-ci/README.md
@@ -6,10 +6,11 @@ GitLab CI jobs run in a Docker image, defined here. To update that image
 (perhaps to install some more packages):
 
 1. Edit `.gitlab-ci/Dockerfile` with the changes you want
-1. Run `.gitlab-ci/run-docker.sh build --base=debian --base-version=1` to build
-   the new image (bump the version as needed)
-1. Run `.gitlab-ci/run-docker.sh push  --base=debian --base-version=1` to upload
-   the new image to the GNOME GitLab Docker registry
+1. Run `.gitlab-ci/run-docker.sh build --base=debian-stable --base-version=1` to
+   build the new image (bump the version from the latest listed for that `base`
+   on https://gitlab.gnome.org/GNOME/glib/container_registry)
+1. Run `.gitlab-ci/run-docker.sh push  --base=debian-stable --base-version=1` to
+   upload the new image to the GNOME GitLab Docker registry
     * If this is the first time you're doing this, you'll need to log into the
       registry
     * If you use 2-factor authentication on your GNOME GitLab account, you'll