Update docs

docs/source/core/io.md

@@ -39,13 +39,13 @@ DeepMR also contains generic I/O routines that can be used to write custom I/O f
 
 ```python
 # Custom reading routines
-data, head = read_custom_rawdata(filepath, *args, **kwargs) # k-space
-image, head = read_custom_image(filepath, *args, **kwargs) # image
+data, head = read_custom_rawdata(filepath, *args, head=None, **kwargs) # k-space
+image, head = read_custom_image(filepath, *args, head=None, **kwargs) # image
 head = read_custom_acqheader(filepath, *args, **kwargs) # header
 
 # Custom writing routines
-write_custom_rawdata(filepath, data, *args, head=None **kwargs) # k-space
-write_custom_image(filepath, image, *args, head=None, **kwargs) # image
+write_custom_rawdata(filepath, data, *args, **kwargs) # k-space
+write_custom_image(filepath, image, *args, **kwargs) # image
 write_custom_acqheader(filepath, head, *args, **kwargs) # header
 ```