Add a README file for RISC-V specific kernel selftests under tools/testing/selftests/riscv/. This mirrors the existing README for arm64, providing clear guidance on how the tests are architecture specific and skipped on non-riscv systems. It also includes standard make commands for building, running and installing the tests, along with a reference to general kselftest documentation. Signed-off-by: Bala-Vignesh-Reddy <reddybalavignesh9979@gmail.com> Reviewed-by: Andrew Jones <ajones@ventanamicro.com> Link: https://lore.kernel.org/r/20250815180724.14459-1-reddybalavignesh9979@gmail.com Signed-off-by: Paul Walmsley <pjw@kernel.org>