forked from Mirrors/opensbi

This commit adds a new GitHub Actions workflow for repository lockdown. The workflow triggers when a pull request is opened, and it notifies the contributor to use the OpenSBI mailing list for patch reviews. Additionally, the .gitignore file is updated to include the .github directory. Signed-off-by: Dongdong Zhang <zhangdongdong@eswincomputing.com> Reviewed-by: Anup Patel <anup@branifault.org>