CI: Add note on deploy api_key

.travis.yml

@@ -352,6 +352,7 @@ after_failure: |
 deploy:
   provider: releases
   api_key:
+    # Uses token from user open62541-travis-release (managed by @Pro)
     secure: dtn6ayBGoWzeVMM6xYpSRZly1XOhS/2jdiwEHd0hYZIr0dNq18CxTiqbGrUwW1JsSiXoHaGSZhUVr06O1P/tfC3Ma6i7ugyun+yXz6FdZiwirjURI8HQe+XwR4Ui3hqgQSOHLMK/xtOkjM28AN1jg9u3//Zep69xJVIGAqNT0bE=
   file:
     - open62541-win32.zip