Update docstring

scripts/dxf_to_csv.py

@@ -1,11 +1,27 @@
 """Extract points from a dxf file, and save in csv format
 
-Example:
+usage:
-    Extract coordinates from all layers
+  dxf_to_csv.py [-h] [-n LAYER_NAME] [-l] dxf_name
-    > python dxf_to_xyz.py file.dxf
+
+positional arguments:
+  dxf_name       path to dxf file
+
+optional arguments:
+  -h, --help     show this help message and exit
+  -n LAYER_NAME  name of layer
+  -l             show list of layers
+
+Examples:
+
+Show available layers:
+> python dxf_to_csv.py drawing.dxf -l
+
+Convert all layers:
+> python dxf_to_csv.py drawing.dxf
+
+Convert specific layer:
+> python dxf_to_csv.py drawing.dxf -n LAYER_NAME
 
-    Extract coordinates from one layer
-    > python dxf_to_xyz.py file.dxf 'survey'
 """
 
 __author__ = "D. Howe"