doc: Add description and key features section to README

README.md

@@ -2,6 +2,20 @@
 
 Organize groups of scripts into documented CLIs with subcommands.
 
+`sub` is a tool designed to help organize groups of scripts into a command-line
+interface (CLI) with subcommands. It allows the dynamic creation of a CLI from
+a directory (and subdirectories) of scripts.
+
+## Key features
+
+- **Easy to setup**: A single command is required to setup.
+- **Display help**: Display usage and documentation for scripts.
+- **Validate arguments**: Validate arguments to scripts based on documentation.
+- **Parse arguments**: Automatically parse arguments to scripts so getopts is not needed.
+- **Nested subcommands**: Supports nested directories for hierarchical command structures.
+- **Aliases**: Supports aliases for subcommands.
+- **Cross-platform**: Works on Linux and macOS.
+
 ## Overview
 
 `sub` is meant to be used as the entry point for a CLI. Given the following