Add Security Policy

[maennchen]

Changes

Adds a Security Policy to the project.

It will be shown:

• On the repository homepage on the right next to the Code of conduct
• In the security tab

Policy

The security policy contents are my personal recommendation and also mirrors what we applied at the EEF.

It links to the OpenSSF Vulnerability Guide which explains how the project and the finder of the issue should behave.

I recommend reading the maintainer guide for context: https://github.com/ossf/oss-vulnerability-guide/blob/main/maintainer-guide.md

TODO

• Check if the proposed policy is a good fit
• Decide who will handle reports
• Create [email protected] email or adapt to another one that works
• Check if you want to cover the whole organization (https://github.com/gleam-lang/.github) or just this repo