[Buildah] Buildah v1.21.0 Release Announcement

Hi All,     Buildah v1.21.0 is now available and we've just posted the Release Announcement with the details at: https://buildah.io/releases/2021/06/09/Buildah-version-v1.21.0.html.     There's now a new --secret option for the bud command that let's you insert "secret" info into your container image such as a database password, yet not have it visible to anyone within the container.  Also the "buildah manifest rm" command has been added to allow you to remove one ore more manifests from an image, and a lot of work under the covers to make the image operations faster and the code usable across the container projects.  Plus a number of smaller fixes and improvements throughout.     Thanks to the many contributors for their help and contributions!     Best Wishes,     t