Document training subcommands

Documentation about training subcommands were missing.

dan/ocr/line/__init__.py

@@ -7,7 +7,7 @@ from dan.ocr.line.train import run as run_train
 def add_generate_parser(subcommands) -> None:
     parser = subcommands.add_parser(
         "generate",
-        description=__doc__,
+        description="Generate synthetic data to train DAN models.",
         help="Generate synthetic data to train DAN models.",
     )
     parser.set_defaults(func=run_generate)
@@ -16,7 +16,7 @@ def add_generate_parser(subcommands) -> None:
 def add_line_parser(subcommands) -> None:
     parser = subcommands.add_parser(
         "line",
-        description=__doc__,
+        description="Train a DAN model at line level",
         help="Train a DAN model at line level.",
     )
     parser.set_defaults(func=run_train)