Added a basic SECURITY.md.

Author: daveverwer

SECURITY.md

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+# Security Policies and Procedures
+
+This document outlines security procedures and general policies for the Swift Package Index project.
+
+## Reporting a Bug
+
+We take all security bugs in the Swift Package Index project seriously. We appreciate your responsible disclosure efforts and will acknowledge your contributions where appropriate.
+
+Report security bugs via the “[Security](https://github.com/SwiftPackageIndex/SwiftPackageIndex-Server/security)” tab in our GitHub repository or via the “[Report a Vulnerability](https://github.com/SwiftPackageIndex/SwiftPackageIndex-Server/security/advisories/new)” form. This will open a private conversation to report and discuss the vulnerability with project maintainers.
+
+Once we resolve a security issue, where appropriate, we will publish a security advisory on the GitHub repository’s “Security” tab.
+
+## Comments on this Policy
+
+Please [open a discussion](https://github.com/SwiftPackageIndex/SwiftPackageIndex-Server/discussions/new/choose) if you have suggestions to improve this process.