lighter image, add link to doc for base image

Dockerfile

 # Build image from the base image, previously configured for you
-# FROM registry-gitlab.pasteur.fr/hub/shiny-k8s/r:3.6.3
-# FROM registry-gitlab.pasteur.fr/hub/shiny-k8s/r:4.2.3
-FROM registry-gitlab.pasteur.fr/hub/shiny-k8s/r:4.3.1
+# Full list of images can be found at 
+# https://hub.pages.pasteur.fr/shiny-k8s/user_guide/configure_image.html#image-list
+FROM registry-gitlab.pasteur.fr/hub/shiny-k8s/r:4.3.1--1.5.22.1017
 
 # Add workdir information
 WORKDIR /srv/shiny-server/
 
-# Install additional dependencies, comment the block if you don't have one
-RUN apt-get update \
- && apt-get install -y \
-        wget \
- && rm -rf /var/lib/apt/lists/*
+# Install additional dependencies, uncomment the block if you have one, and edit/duplicate line 12
+# RUN apt-get update \
+#  && apt-get install -y \
+#         your-system-dependency \
+#  && rm -rf /var/lib/apt/lists/*
 
 # Copy your dependencies, destination filename must be "packages_to_install.csv"
 COPY ./my_packages_to_install.csv /opt/scripts/packages_to_install.csv