Introduction sigstore-c

These days, there’s many interoperable Sigstore client libraries in various programming languages. But there are still a few places where you might struggle to run Sigstore, like on a Intel 8086 processor (first released in 1978), say running a version of DOS. Until today. Introducing sigstore-c, which focuses on portability over features (and correctness!) You can build sigstore-c on any system with a C89 compiler, including modern Linux environments with gcc or the aforementioned DOS environment with something like Open Watcom v2.