new: print usage section in help !minor

Signed-off-by: Valentin Lab <valentin.lab@kalysto.org>

bin/compose-core

@@ -117,12 +117,6 @@ clean_cache() {
 }
 
 
-usage="$exname SERVICE"'
-
-Deploy and manage a swarm of containers to provide services based on
-a ``compose.yml`` definition and charms from a ``charm-store``.
-'
-
 export DEFAULT_COMPOSE_FILE
 
 ##
@@ -3579,6 +3573,8 @@ get_docker_charm_action_help() {
 
 display_help() {
     print_help
+    echo "${WHITE}Usage${NORMAL}:"
+    echo "  $usage"
     echo "${WHITE}Options${NORMAL}:"
     echo "  -h, --help                  Print this message and quit"
     echo "                              (ignoring any other options)"