Create SECURITY.md (#25)

## Security Update: XSS Vulnerability Fix

We have released a new version (1.0.3) that addresses a critical security vulnerability related to cross-site scripting (XSS). The issue was found in the `errmsg` parameter handling in the login endpoint.

### Affected Versions
- Versions 1.0.2 and below

### Fixed Versions
- Version 1.0.3

### Recommended Actions
We strongly recommend all users to update to the latest version (1.0.3) immediately. You can update your project by following the instructions in our documentation.

### Reporting Security Issues
If you find any security issues, please report them to [security@example.com](mailto:jamiesun.net@gmail.com). We appreciate your help in keeping our project secure.

Thank you for your attention to this important update.

- The Security Team

SECURITY.md

@@ -0,0 +1,21 @@
+# Security Policy
+
+## Supported Versions
+
+Use this section to tell people about which versions of your project are
+currently being supported with security updates.
+
+| Version | Supported          |
+| ------- | ------------------ |
+| 5.1.x   | :white_check_mark: |
+| 5.0.x   | :x:                |
+| 4.0.x   | :white_check_mark: |
+| < 4.0   | :x:                |
+
+## Reporting a Vulnerability
+
+Use this section to tell people how to report a vulnerability.
+
+Tell them where to go, how often they can expect to get an update on a
+reported vulnerability, what to expect if the vulnerability is accepted or
+declined, etc.