Add explicit clarification about variable quoting

Closes: #81

README.md

@@ -117,6 +117,8 @@ Example:
                         --mount type=bind,source=/root/.docker/config.json,target=/root/.docker/config.json,ro \
                         containrrr/shepherd
 
+*Note that the quotes in the command above are evaluated by your shell and are not part of the environment variable value! - See also the note in [docker-compose.yml](docker-compose.yml)!*
+
 ## Running on a cron schedule
 
 When running shepherd as described with a `SLEEP_TIME`, the de facto running times will drift the longer the container is running. If you want to run shepherd on a fixed schedule instead, it is recommended to pair it with [swarm-cronjob](https://github.com/crazy-max/swarm-cronjob):

docker-compose.yml

@@ -5,6 +5,10 @@ services:
     build: .
     image: containrrr/shepherd
     environment:
+      # Beware YAML gotchas regarding quoting:
+      # With KEY: 'VALUE', quotes are part of yaml syntax and thus get stripped
+      # but with KEY='VALUE', they are part of the value and stay there,
+      # causing problems!
       TZ: 'US/Eastern'
       SLEEP_TIME: '5m'
       FILTER_SERVICES: ''