(SPIKE) Fix code scanning alert - Security-Policy

[cmwylie19]

Add a Security.md

Tracking issue for:

• https://github.com/defenseunicorns/pepr/security/code-scanning/23

[cmwylie19]

• Creates a preferred method of contact by security researchers in the event of a security vulnerability instead of posting it publicly which could lead to disclosure of vulnerability details.
• They are able to report to us via a simple form
• When a vulnerability is reported, we can accept it, ask more questions, or reject it. If accepted, you are ready to collaborate on a fix.
• Vulnerability is less likely to be in the public eye