RFE: add a list of supported architectures to the README

[vismir2]

Please provide a list of supported architectures. As of now it is hard to tell for what types there is already support.

Also please consider supporting the new open source RISC-V architecture in the future

[pcmoore]

I do make note of new architectures in the CHANGELOG, but I agree we could probably make it more prominent, e.g. in the README.

If you are interested in RISC-V support, please see the existing PR #50, there is still work to be done before we can add libseccomp support. Perhaps you could help that effort?

[pcmoore]

Resolved via c14558e