Change wording based on Thom’s feedback

app/main/views/service_settings.py

@@ -497,6 +497,8 @@ def service_set_sms_prefix(service_id):
         'on' if current_service['prefix_sms_with_service_name'] else 'off'
     ))
 
+    form.enabled.label.text = 'Start all text messages with ‘{}:’'.format(current_service['name'])
+
     if form.validate_on_submit():
         service_api_client.update_service(
             current_service['id'],