Replace all placeholders in SECURITY.md

[masutaka]

For SECURITY.md, I have replaced all necessary parts.

I would especially like a review of whether "3 BUSINESS DAYS" is acceptable.

[vercel]

@masutaka is attempting to deploy a commit to the Edge team on Vercel, but is not a member of this team. To resolve this issue, you can:

• Make your repository public. Collaboration is free for open source and public repositories.
• Add @masutaka as a member. A Pro subscription is required to access Vercel's collaborative features.
  • If you're the owner of the team, click here and add @masutaka as a member.
  • If you're the user who initiated this build request, click here to request access.
  • If you're already a member of the Edge team, make sure that your Vercel account is connected to your GitHub account.

To read more about collaboration on Vercel, click here.

[shige]

✅