Document signing release artifacts

Author: MrAlias

RELEASING.md

@@ -112,6 +112,17 @@ It is critical you make sure the version you push upstream is correct.
 Finally create a Release for the new `<new tag>` on GitHub.
 The release body should include all the release notes from the Changelog for this release.
 
+### Sign the Release Artifact
+
+To ensure we comply with CNCF best practices, we need to sign the release artifact.
+The tarball attached to the GitHub release needs to be signed with your GPG key.
+
+Follow [these steps] to sign the release artifact and upload it to GitHub.
+You can use [this script] to verify the contents of the tarball before signing it.
+
+[these steps]: https://wiki.debian.org/Creating%20signed%20GitHub%20releases
+[this script]: https://github.com/MrAlias/attest-sh
+
 ## Post-Release
 
 ### Contrib Repository