Docs: Update usage instructions in README

This commit updates the README.md file to clarify the usage
instructions for the ai-commit.sh script. It now includes
instructions on how to amend the previous commit using the `-a`
or `--amend` flags. This enhancement provides users with clear
guidance on amending commits, improving the tool's usability.
Additionally, it documents the forwarding of arguments to the
python script.

README.md

@@ -36,12 +36,19 @@ This tool automatically generates Git commit messages based on your staged chang
 ## Usage
 
 1.  **Stage your changes:** Use `git add` to stage the files you want to include in the commit.
-2.  **Run the script:** Execute the `ai-commit.sh` script from the root of your Git repository:
-    ```bash
-    ./ai-commit.sh
-    ```
+2.  **Run the script:**
+    *   **For a new commit:** Execute the `ai-commit.sh` script from the root of your Git repository:
+        ```bash
+        ./ai-commit.sh
+        ```
+    *   **To amend the previous commit:** Use the `-a` or `--amend` flag:
+        ```bash
+        ./ai-commit.sh -a
+        # or
+        ./ai-commit.sh --amend
+        ```
 3.  **Review and Confirm:** The script will:
-    - Fetch the staged diff.
+    - Fetch the staged diff (for a new commit) or the diff representing the changes to be amended (for an amend).
     - Generate a commit message using the Gemini API.
     - Print the generated message.
     - Ask for your confirmation (`y/n`).
@@ -53,12 +60,14 @@ This tool automatically generates Git commit messages based on your staged chang
 2.  It mounts the current directory (`pwd`) as `/repo` inside the container, allowing the script to access your Git repository.
 3.  It mounts your `.gitconfig` and `.git-credentials` (read-only) for Git operations within the container.
 4.  It passes the `GEMINI_API_KEY` environment variable into the container.
-5.  The `git_commit_ai.py` script:
+5.  It forwards any arguments passed to `ai-commit.sh` (like `-a` or `--amend`) to the Python script inside the container.
+6.  The `git_commit_ai.py` script:
+    - Parses command-line arguments (e.g., `--amend`).
     - Retrieves the staged diff using `git diff --staged`.
     - Sends the diff to the Gemini API with a prompt asking for a commit message.
     - Receives the generated message.
-    - Prompts the user for confirmation.
-    - If confirmed, runs `git commit -m "..."` with the generated message.
+    - Prompts the user for confirmation (mentioning if it's an amend).
+    - If confirmed, runs `git commit -m "..."` or `git commit --amend -m "..."` with the generated message.
 
 ## Files