Update README.md to enhance usage instructions and clarify container functionality

README.md

@@ -1,3 +1,20 @@
 # Azure CLI container
 
+This repository contains a Dockerfile for building an Azure CLI container image.
 
+It is designed to be used as a operating environment for running Azure CLI commands,
+while providing isolation from the host system. User's home directory is mounted
+into the container to persist configuration and credentials. Volume is used to
+persist home directory data.
+
+## Usage
+
+```bash
+azure-cli [--account ACCOUNT_NAME] [--user CONTAINER_USERNAME] [ container CLI arguments... ]
+```
+
+- `--account ACCOUNT_NAME` - Specify the account name to use for the volume that stores the home directory data. Defaults to the current user's username.
+- `--user CONTAINER_USERNAME` - Specify the username to use inside the container. Defaults `ubuntu`.
+- `container CLI arguments...` - Any additional arguments are passed to the container CLI command (not the command inside the container).
+
+> **Note:** Copy the `azure-cli` script to a directory in your `PATH` (e.g. `/usr/local/bin`) to use it as a regular command.