Revise SECURITY.md for security issue reporting

Updated the SECURITY.md file to focus on reporting security issues and removed sections about supported versions and reporting vulnerabilities.

Author: bobsingor

SECURITY.md

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+# Reporting Security Issues
+
+If you believe you have found a security vulnerability in EmbedPDF, we appreciate your help in disclosing it to us responsibly.
+
+We take all reports seriously and will investigate them promptly. We are committed to working with you to understand and resolve any legitimate issues quickly.
+
+Please report any potential vulnerabilities privately to **[email protected]**.
+
+**Please do not** disclose security issues in public GitHub issues.