Docs: Simplify SECURITY.md.

Author: JiaT75

.github/SECURITY.md

@@ -16,13 +16,7 @@ the chance that the exploit will be used before a patch is released.
 You may submit a report by emailing us at
 [xz@tukaani.org](mailto:xz@tukaani.org), or through
 [Security Advisories](https://github.com/tukaani-project/xz/security/advisories/new).
-While both options are available, we prefer email. In any case, please
-provide a clear description of the vulnerability including:
-
-- Affected versions of XZ Utils
-- Estimated severity (low, moderate, high, critical)
-- Steps to recreate the vulnerability
-- All relevant files (core dumps, build logs, input files, etc.)
+While both options are available, we prefer email.
 
 This project is maintained by a team of volunteers on a reasonable-effort
 basis. As such, please give us 90 days to work on a fix before