update leo-package README

package/README.md

@@ -4,6 +4,27 @@
 [![Authors](https://img.shields.io/badge/authors-Aleo-orange.svg)](../AUTHORS)
 [![License](https://img.shields.io/badge/License-GPLv3-blue.svg)](./LICENSE.md)
 
-This module defines the structure of a Leo project package.
+## Description
 
-Each file in this directory mirrors a corresponding file generated in a new Leo project package.
+This module defines the structure of a Leo project package. And describes behavior of package internals, such
+as Leo Manifest (Leo.toml), Lock File (Leo.lock), source files and imports. 
+
+Mainly used by Leo binary.
+
+## Structure
+
+Each directory in this crate mirrors a corresponding file generated in a new Leo project package:
+
+```
+package/src
+├── errors  # crate level error definitions
+├── imports # program imports management
+├── inputs  # program inputs directory
+├── outputs # program outputs directory
+├── root    # program root: Leo.toml, Leo.lock 
+└── source  # source files directory
+```
+
+## Testing
+
+Package features functional tests in the `tests/` directory.