update readme

README.md

@@ -5,7 +5,7 @@ Download entire projects from openneuro.org. All you need is a dataset ID.
 ## Usage
 
 ```
-usage: openneuro-dl [-h] [--savepath SAVEPATH] id
+usage: openneuro_dl [-h] [--savepath SAVEPATH] [--savename SAVENAME] [--w] id
 
 download a dataset from openneuro.org
 
@@ -16,6 +16,9 @@ positional arguments:
 optional arguments:
   -h, --help           show this help message and exit
   --savepath SAVEPATH  the output directory where you would like to download
-                       the dataset (default is the current working directory +
-                       the dataset id)
+                       the dataset (default is the current working directory)
+  --savename SAVENAME  savename is an optional name to give the downloaded
+                       dataset folder. The default is the dataset id.
+  --w                  re-sync existing dataset with the same ID if it already
+                       exists in the savepath
 ```