[mutter] ci/Dockerfile: Add commands for regenerating

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit fefac75e96b7d400ae032fbc5b44a9df93143945
Author: Jonas Ådahl <jadahl gmail com>
Date:   Wed Jun 26 11:19:24 2019 +0200

    ci/Dockerfile: Add commands for regenerating
    
    Instead of either figuring out themself, or looking at the commit that
    added the file, just make life easier by providing the commands for
    rebuilding and pushing as a comment in the Dockerfile itself.
    
    https://gitlab.gnome.org/GNOME/mutter/merge_requests/648

 .gitlab-ci/Dockerfile | 7 +++++++
 1 file changed, 7 insertions(+)
---
diff --git a/.gitlab-ci/Dockerfile b/.gitlab-ci/Dockerfile
index 6b413bb35..5bae53be9 100644
--- a/.gitlab-ci/Dockerfile
+++ b/.gitlab-ci/Dockerfile
@@ -1,3 +1,10 @@
+# Rebuild and push with
+#
+#     cd .gitlab-ci/
+#     docker build -t registry.gitlab.gnome.org/gnome/mutter/master:v2 .
+#     docker push registry.gitlab.gnome.org/gnome/mutter/master:v2
+#
+
 FROM fedora:30
 
 RUN dnf -y update && dnf -y upgrade && \