Signed pushes for kernel.org

Kernel.org manager Konstantin Ryabitsev describesthe Git signed-push functionality, which is now supported by thekernel.org system. "To help hedge against this problem, git providesdevelopers a way to sign their actual pushes, as a means to attest 'yes, Iactually did intend to push these commits into this ref in this repositoryon this server, and here's my PGP signature to prove it.'" Amongother things, these signatures can be preserved in a commit transparencylog, whichis also now provided by kernel.org.