Document --debug voodoo :)

letsencrypt/cli.py

@@ -843,7 +843,8 @@ def prepare_and_parse_args(plugins, args):
         "really know what you're doing!")
     helpful.add(
         "testing", "--debug", action="store_true",
-        help="Show tracebacks if the program exits abnormally")
+        help="Show tracebacks in case of errors, and allow execution on "
+             "experimental platforms")
     helpful.add(
         "testing", "--no-verify-ssl", action="store_true",
         help=config_help("no_verify_ssl"),