Update readme

Author: dyollb

README.md

@@ -7,7 +7,7 @@
 
 ## Overview
 
-Create [Typer](https://github.com/tiangolo/typer) command line interface from functions that use [SimpleITK](https://github.com/SimpleITK/SimpleITK) images (and transforms) as arguments or return type.
+Create [Typer](https://github.com/tiangolo/typer) command line interface from functions that use [SimpleITK](https://github.com/SimpleITK/SimpleITK) images (and transforms) as arguments or return type. 
 
 ```Python
 import SimpleITK as sitk
@@ -32,6 +32,8 @@ if __name__ == "__main__":
     app()
 ```
 
+To work, sitk-cli inspects the type annotations of the function and creates a wrapper function that loads images from file and passes these to the original function. Returned images (transforms) are written to a file by the wrapper function..
+
 ## Installation
 
 ```sh