Add click annotations for VCF path

Author: jeromekelleher

bio2zarr/cli.py

@@ -517,7 +517,7 @@ def plink2zarr():
 
 @click.command
 @version
-@click.argument("vcf_path", type=click.Path())
+@click.argument("vcf_path", type=click.Path(exists=True, dir_okay=False))
 @verbose
 @click.option(
     "-n",