Improve Docker and proxy documentation

example.env

@@ -26,10 +26,19 @@ USER_TIME_ZONE=Europe/Berlin
 FORCE_DEBUG_TOOLBAR=false
 BACKUP_DIR=/mnt/backups
 
-# Docker swarm mode does not respect the Docker Proxy client configuration
-# (see https://docs.docker.com/network/proxy/#configure-the-docker-client).
-# So we have to set those environment variables ourselve if necessary.
-# HTTP_PROXY=http://user:pass@myproxy.net:8080
+# Docker Compose does automatically set http_proxy, HTTP_PROXY, https_proxy,
+# HTTPS_PROXY, no_proxy and NO_PROXY with the values specified in
+# ~/.docker/config.json. Unfortunately Docker Swarm does not set those value,
+# but those can be set by the environment variables in the env file.
+# If those are set in Docker Compose mode the ones here overwrite those
+# in the config.json file.
+# Cave, those variables here doesn't have any effect when the image is build
+# (only those in the config.json file work).
+# See also https://docs.docker.com/network/proxy/#configure-the-docker-client
+# and https://forums.docker.com/t/docker-swarm-mode-not-picking-up-proxy-configuration/132233/8?u=medihack
 # http_proxy=http://user:pass@myproxy.net:8080
-# HTTPS_PROXY=http://user:pass@myproxy.net:8080
+# HTTP_PROXY=http://user:pass@myproxy.net:8080
 # https_proxy=http://user:pass@myproxy.net:8080
+# HTTPS_PROXY=http://user:pass@myproxy.net:8080
+# no_proxy=
+# NO_PROXY=