feat(cli): add a small hello command

Show a minimal subcommand pattern without turning the template into a demo app.

Author: yujeongdev

README.md

@@ -20,6 +20,13 @@ cheap enough to run all the time.
 make setup-dev
 make check
 python -m python_template --help
+python -m python_template hello
+```
+
+Sample output:
+
+```text
+Let's build something fun, Yujeong.
 ```
 
 ## Core commands

src/python_template/__main__.py

@@ -11,15 +11,30 @@
 )
 
 
-@click.command(help="Show the template version and default tasks.")
-def cli() -> None:
-    """Print the template version and recommended first commands."""
+@click.group(
+    invoke_without_command=True,
+    context_settings={"help_option_names": ["-h", "--help"]},
+    help="Show the template defaults and example commands.",
+)
+@click.pass_context
+def cli(ctx: click.Context) -> None:
+    """Run the template CLI."""
+    if ctx.invoked_subcommand is not None:
+        return
+
     click.echo(f"python-template {__version__}")
     click.echo("Default tasks:")
     for task in DEFAULT_TASKS:
         click.echo(f"- {task}")
 
 
+@cli.command()
+@click.option("--name", default="Yujeong", show_default=True, help="Name to greet.")
+def hello(name: str) -> None:
+    """Print a tiny example subcommand."""
+    click.echo(f"Let's build something fun, {name}.")
+
+
 def main() -> None:
     """Run the CLI."""
     cli()

tests/test_cli.py

@@ -30,10 +30,34 @@ def test_module_cli_help_runs() -> None:
         text=True,
     )
 
-    assert "Show the template version and default tasks." in result.stdout
+    assert "Show the template defaults and example commands." in result.stdout
     assert "Usage:" in result.stdout
 
 
+def test_module_cli_hello_runs_with_default_name() -> None:
+    """Run the example hello command with the default name."""
+    result = subprocess.run(
+        [sys.executable, "-m", "python_template", "hello"],
+        check=True,
+        capture_output=True,
+        text=True,
+    )
+
+    assert "Let's build something fun, Yujeong." in result.stdout
+
+
+def test_module_cli_hello_accepts_a_custom_name() -> None:
+    """Run the example hello command with an explicit name."""
+    result = subprocess.run(
+        [sys.executable, "-m", "python_template", "hello", "--name", "friend"],
+        check=True,
+        capture_output=True,
+        text=True,
+    )
+
+    assert "Let's build something fun, friend." in result.stdout
+
+
 def test_package_exports_version() -> None:
     """Expose the package version at the top level."""
     assert __version__ == "0.1.0"