[ci] Provide helpful hint in trigger_deb stage

.gitlab-ci.yml

@@ -131,6 +131,7 @@ trigger_deb:
   image: registry.0xacab.org/leap/docker/buster_amd64:latest
   stage: trigger
   script:
+    - echo "Triggering CI pipeline on https://0xacab.org/leap/riseup-vpn_package/pipelines"
     - "curl -X POST -F token=$RISEUP_VPN_DEB_TRIGGER_TOKEN -F ref=master https://0xacab.org/api/v4/projects/1916/trigger/pipeline"
 
 vendorize: