Automated update of `README.md` for release 8.2.1Co-authored-by: keith <keith@users.noreply.github.com>

Use -prune to handle excluded paths, rather than simply ! -path, whichwill still visit all subdirectories and files in the excluded paths.This is more efficient, but more importantly avoids visiting files whichmay not be readable by the user, which causes `find` fail, and causesbuildifier to fail as we are using `-o pipefail`.

Recently, riscv64 has gained widespread adoption, and we can consideradding support for it to `buildifier-prebuilt`.The upstream `bazelbuild/buildtools` that we depend on has already addedriscv64 support, so we don't need many modifications to complete supportfor riscv64.I ran the CI in my own fork, and the results show everything wentsmoothly. For details, please seehttps://github.com/ffgan/buildifier-prebuilt/actions/runs/19956694354I also tested it on my riscv64 machine, and the results likewiseindicate everything went smoothly.If you have any questions about the above, please @ me directly. I'mhappy to answer any related questions.---**Other Info**Co-authored by: nijincheng@iscas.ac.cn;Signed-off-by: ffgan <sudoemt@gmail.com>