Add new configuration variable to .env template

.env.tpl

@@ -21,6 +21,9 @@ HOST_DOCKER_GID=
 # NOTES: Use `.` as <project-basedir>
 # HOST_LOG_DIR=
 
+# DEFAULT: nopaque_default
+# DOCKER_NETWORK_NAME=
+
 ################################################################################
 # Flask                                                                        #
 # https://flask.palletsprojects.com/en/1.1.x/config/                           #
@@ -186,4 +189,4 @@ NOPAQUE_DOCKER_REGISTRY_PASSWORD=
 
 # READ-COOP account data: https://readcoop.eu/
 # NOPAQUE_READCOOP_USERNAME=
-# NOPAQUE_READCOOP_PASSWORD=
+# NOPAQUE_READCOOP_PASSWORD=
\ No newline at end of file