support/docker: don't use sudo to build

On a properly setup machine, it is totally useless to use sudo to run
docker; it is very bad practice. Instead, users really should add
themselves to the docker group.

Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Cc: Romain Naour <romain.naour@gmail.com>
Cc: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Reviewed-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
(cherry picked from commit 9f6a2dbe030b10eda2797430a87fffc34f8c4685)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

support/docker/Dockerfile

@@ -1,7 +1,7 @@
 # This Dockerfile generates the docker image that gets used by Gitlab CI
 # To build it (YYYYMMDD.HHMM is the current date and time in UTC):
-#   sudo docker build -t buildroot/base:YYYYMMDD.HHMM support/docker
-#   sudo docker push buildroot/base:YYYYMMDD.HHMM
+#   docker build -t buildroot/base:YYYYMMDD.HHMM support/docker
+#   docker push buildroot/base:YYYYMMDD.HHMM
 
 # We use a specific tag for the base image *and* the corresponding date
 # for the repository, so do not forget to update the apt-sources.list