Push Dockerhub README.md file on release

Add stage 'readme' and job 'readme_docker_release_tag' to push the file 'docker/README.md' to the team's duniter-v2s repo.

The job uses chko/docker-pushrm and is adapted from the related Gitlab CI/CD example.

See https://github.com/christian-korneck/docker-pushrm

docker/compose/gdev-mirror.docker-compose.yml

 # This is a docker template for running a gdev mirror
-# You should write a .env file aside with the environment variables:
-#
-# --- .env ---
-# SERVER_DOMAIN=gdev.example.com
-# PEER_ID=1234XxxXXxxXxxxXxzbQqEkEpTPxD9S1PtpzkZSYoueyERA5vVtQ
-# ------------
-#
-# The peer id has to be replaced withe the output of the following command
-#
-# >>> PEER_ID >>>
-# docker run --rm -it --entrypoint duniter -v $PWD:/var/lib/duniter/  duniter/duniter-v2s:v0.3.0 key generate-node-key --file /var/lib/duniter/node.key
-# <<<<<<<<<<<<<<<
 
-
-version: "3.4"
+version: "3.5"
 
 services:
   duniter-rpc:
@@ -38,8 +25,7 @@ services:
       - "/var/lib/duniter/node.key"
       - "--public-addr"
       # SERVER_DOMAIN should be replaced by a domain name that point on your server
-      # PEER_ID should be replaced by the output of the command given at the top of this file
-      - "/dns/${SERVER_DOMAIN?SERVER_DOMAIN should be set}/tcp/30333/p2p/${PEER_ID?PEER_ID should be set}"
+      - "/dns/${SERVER_DOMAIN?SERVER_DOMAIN should be set}/tcp/30333/ws"
       - "--rpc-cors"
       - "all"