Expand SECURITY.md with incident response plan

[perminder-17]

This PR expands SECURITY.md with the vulnerability reporting and incident response process.

PR Checklist

• npm run lint passes
• [Inline reference] is included / updated
• [Unit tests] are included / updated

[p5-bot]

Continuous Release

CDN link

• https://raw.esm.sh/pr/p5@d490794/lib/p5.min.js

Published Packages

• https://pkg.pr.new/p5@d490794

Commit hash: d490794

Previous deployments

66f5f50

• https://raw.esm.sh/pr/p5@66f5f50/lib/p5.min.js
• https://pkg.pr.new/p5@66f5f50

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This is an automated message.

[ksen0]

Thanks for adding this one @perminder-17 ! For context, this is a public version of an internal document, which has been reviewed by Processing Foundation staff, and the p5.js maintainers/stewards who work on fixes.