docs: improve note about potential issues when running multiple Postg…

…res instances on the same host (e.g. during development)

support/deployment/README.md

@@ -222,7 +222,7 @@ You can use the `support/scripts/systemd-container-service-file-generate` to eas
     - `--prod` - Configures Traefik to work in a production environment.
       - Supports HTTPS certificates via Let's Encrypt
 
-**NOTE:** If using a Postgres container alongside this service, it may be easier to preserve your dotenv file's Postgres settings when creating your container service, so that the default `localhost` Postgres dev server doesn't interfere with the container network's Postgres server, whose hostname is set to `postgres`.
+**NOTE:** If using a Postgres container alongside this service, make sure you don't mix up the `POSTGRES_HOST` variables if running multiple instances of the same service simulataneously (e.g. in development). An apparent Postgres connection error may just be a value you forgot to change (or change back) when you were updating the dotenv file so you could get the service up and running. (This one has bitten me a couple times.)
 
 - e.g. `POSTGRES_DB=postgres DATABASE_URL=ecto://postgres:postgres@postgres/todo_list ./support/scripts/systemd-container-service-file-generate --postgres --traefik-client`