Add security policy (#12687)

[Christian Brabandt]

Add security policy (#12687)

Commit: https://github.com/vim/vim/commit/6ec7808c4a469d1fe22101f75e4d9abc269823a6
Author: Santos Gallegos <sts...@proton.me>
Date: Wed Aug 9 13:11:37 2023 -0500

Add security policy (https://github.com/vim/vim/issues/12687)

* Add security policy

Currently is hard to find where to report security issues,
the only mention of it is in the issue template.

https://github.com/vim/vim/blob/4c0089d696b8d1d5dc40568f25ea5738fa5bbffb/.github/ISSUE_TEMPLATE/bug_report.yml?plain=1#L12-L15

Adding a SECURITY.md file will make it easier to find,
it will be displayed in https://github.com/vim/vim/security.

* Mention that reports are private

diff --git a/SECURITY.md b/SECURITY.md
new file mode 100644
index 000000000..7d9c77d27
--- /dev/null
+++ b/SECURITY.md
@@ -0,0 +1,8 @@
+# Security Policy
+
+## Reporting a vulnerability
+
+If you want to report a security issue, please use [huntr.dev](https://huntr.dev/bounties/disclose?target=https%3A%2F%2Fgithub.com%2Fvim%2Fvim) to privately disclose the issue to us.
+They also have rewards in the form of money, swag and CVEs.
+
+**Please don't publicly disclose the issue until it has been addressed by us.**