Update docstring

scripts/photo_to_kml.py

@@ -3,10 +3,19 @@
 This script takes a folder of images, and creates a placemark with a thumbnail
 of each image, based on the GPS coordinates in the EXIF tags.
 
+Usage:
+  photo_to_kml.py [-h] IMAGE_FOLDER
+
+Positional arguments:
+  IMAGE_FOLDER  name of input folder
+
+Optional arguments:
+  -h, --help    show this help message and exit
+
 Examples:
 
-Create a kml for a folder of photos, named 'images'.
+Create a kml for a folder of photos, named 'image_folder'.
-    > python photo_to_kml.py images
+> python photo_to_kml.py image_folder
 
 """
 
@@ -127,9 +136,12 @@ def export_kml_file(dirname, fnames, dirname_thumbs, kml_name):
 
 
 def main():
-    parser = argparse.ArgumentParser(usage=__doc__)
+    parser = argparse.ArgumentParser()
     parser.add_argument(
-        'folder', nargs='?', help='name of input folder', default=None)
+        'folder',
+        metavar='IMAGE_FOLDER',
+        help='name of input folder',
+        default=None)
     args = parser.parse_args()
 
     # Get files in image directory