docs(readme): enhance documentation for apter-tech/ssh-agent action (#8)

- Expanded README to include detailed usage examples for integrating apter-tech/ssh-agent into GitHub workflows.
- Added sections for:
  - Features: Highlights SSH agent integration, host verification, key type filtering, and post-job cleanup.
  - Usage: Demonstrates basic and advanced configurations, including predefined known hosts.
  - Inputs: Lists new and inherited inputs with detailed descriptions.
  - Security Considerations: Emphasizes host key verification practices.
  - Development: Provides an overview of core scripts for contributors.
  - Included a license note for clarity on usage rights.

This update provides comprehensive guidance for users and contributors, improving clarity and ease of use.

Author: warnyul

README.md

@@ -1,2 +1,106 @@
-# ssh-agent
-GitHub Action to setup `ssh-agent` with a private key and host verification
+# apter-tech/ssh-agent
+
+An advanced extension of [webfactory/ssh-agent](https://github.com/webfactory/ssh-agent) that not only manages SSH private key loading but also handles SSH host verification by setting up and cleaning `known_hosts`. This action simplifies secure communication in your workflows by automating host key management with enhanced security checks.
+
+---
+
+## Features
+
+- **SSH Agent Integration**: Extends `webfactory/ssh-agent` to load SSH private keys seamlessly.
+- **Host Verification**:
+  - Automatically fetches SSH host keys using `ssh-keyscan`.
+  - Supports predefined `known_hosts` entries.
+  - Warns about potential security risks for unverified keys.
+- **Key Type Filtering**: Optionally specify the types of keys to fetch (`ecdsa`, `ed25519`, etc.).
+- **Post-Job Cleanup**: Automatically removes added host entries after the job completes.
+
+---
+
+## Usage
+
+Here’s how to integrate the `apter-tech/ssh-agent` action into your GitHub workflows:
+
+### Basic Example
+
+```yaml
+name: Example Workflow
+on: [push, pull_request]
+
+jobs:
+  example:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+      - name: Setup SSH Agent and Host Verification
+        uses: apter-tech/ssh-agent@v1
+        with:
+          ssh-private-key: ${{ secrets.SSH_PRIVATE_KEY }}
+          ssh-host: github.com
+          ssh-key-type: ed25519
+```
+
+## Inputs
+
+### New Inputs
+
+| Name            	| Description                                                                                             	| Required 	| Default   	|
+|-------------------|-----------------------------------------------------------------------------------------------------------|-----------|---------------|
+| ssh-host        	| Hostname to fetch SSH keys from using `ssh-keyscan`.                                                    	| No       	|           	|
+| ssh-key-type    	| Specify the type of key to fetch. Possible values: `ecdsa`, `ed25519`, `ecdsa-sk`, `ed25519-sk`, `rsa`. 	| No       	| All types 	|
+| ssh-known-hosts 	| Predefined `known_hosts` entries. If provided, skips `ssh-keyscan`.                                     	| No       	|           	|
+
+### Inherited Inputs from `webfactory/ssh-agent`
+
+| Name               | Description                                     | Required | Default |
+|--------------------|-------------------------------------------------|----------|---------|
+| `ssh-private-key`  | Private SSH key to register in the SSH agent.   | Yes      |         |
+| `ssh-auth-sock`    | Location of the SSH agent auth socket.          | No       |         |
+| `log-public-key`   | Log public key fingerprints.                    | No       | true    |
+| `ssh-agent-cmd`    | Command to start the SSH agent.                 | No       |         |
+| `ssh-add-cmd`      | Command to add the SSH key to the agent.        | No       |         |
+| `git-cmd`          | Command to use for Git operations.              | No       |         |
+
+## Security Considerations
+
+### Host Key Verification
+- **Recommended:** Always verify host keys manually before using `ssh-keyscan`.
+- **Warnings:** The action emits warnings if unverified host keys are used, as they pose a risk of man-in-the-middle attacks.
+
+## How It Works
+
+**1. Main Workflow:**
+
+- Loads the SSH private key using `webfactory/ssh-agent`.
+- Configures `known_hosts`:
+  - Uses predefined entries if `ssh-known-hosts` is set.
+  - Fetches host keys using `ssh-keyscan` if `ssh-host` is provided.
+
+**2.	Post-Job Cleanup:**
+
+- Removes the last added entry from known_hosts to keep the environment clean.
+
+## Example with Predefined Known Hosts
+
+```yaml
+- name: Setup SSH Agent with Predefined Known Hosts
+  uses: apter-tech/ssh-agent@v1
+  with:
+    ssh-private-key: ${{ secrets.SSH_PRIVATE_KEY }}
+    ssh-known-hosts: |
+      github.com ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIGh4DoiJkCQJklXG3zjGhheklNSklai38skjdjz89
+```
+
+## Development
+
+### Scripts Overview
+- `action.sh`: Main script for handling SSH host setup.
+- `post_action.sh`: Cleanup script to remove temporary host entries.
+
+## Contributing
+
+Contributions are welcome! Please open issues or submit pull requests to improve the functionality or documentation.
+
+## License
+
+This project is licensed under the MIT License. See [LICENSE](LICENSE) for details.