Add warning in the sample configuration file
+# WARNING:
+# Do not use this file as is! It only lists and documents available options
+# without caring about their consistency. Prefer using "opennmt-defaults.yml" as a
+# base configuration and specialize it with addtional configuration files.
+
# The directory where models and summaries will be saved. It is created if it does not exist.
model_dir: toy-ende
