Create SECURITY.md (#32358)

An initial draft of SECURITY.md.

Author: ViralBShah

SECURITY.md

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+# Security Policy
+
+## Supported Versions
+
+The LTS and current stable releases of Julia are the ones supported for security updates.
+
+| Version | Supported          |
+| ------- | ------------------ |
+| LTS     | :white_check_mark: |
+| Stable  | :white_check_mark: |
+| < 1.0   | :x:                |
+
+## Reporting a Vulnerability
+
+Please report security vulnerabilities by emailing [email protected].