Allow using -h for help

It's common to support both `-h` and `--help`. I often find myself using
`ghstack -h` and hitting an error.

Signed-off-by: Daniel Xu <dxu@dxuuu.xyz>

Author: danobi

src/ghstack/cli.py

@@ -48,7 +48,7 @@ def cli_context(
         yield shell, config, github
 
 
-@click.group(invoke_without_command=True)
+@click.group(invoke_without_command=True, context_settings={"help_option_names": ["-h", "--help"]})
 @click.pass_context
 @click.version_option(ghstack.__version__, "--version", "-V")
 @click.option("--debug", is_flag=True, help="Log debug information to stderr")