Publish checksum.txt file with each release

[bizrad]

It would be nice if there was a checksum.txt file with the contents of the sha256 checksums of each released binary.

e.g. for the 1.11.0 release

export BAZELISK_VERSION=1.11.0
for i in bazelisk-darwin bazelisk-darwin-amd64 bazelisk-darwin-arm64 \
bazelisk-linux-amd64 bazelisk-linux-arm64 bazelisk-windows-amd64.exe; do
  curl -LO https://github.com/bazelbuild/bazelisk/releases/download/v${BAZELISK_VERSION}/${i}
done
sha256sum bazelisk-* >checksums.txt

Checksums.txt contents

afb0857e4497810dd9695af2b1491c4184debe45ec035a2bb8a4aeb1542166c4  bazelisk-darwin
c725fd574ea723ab25187d63ca31a5c9176d40433af92cd2449d718ee97e76a2  bazelisk-darwin-amd64
1e18c98312d1a03525f704214304be2445478392c8687888d5d37e6a680f31e6  bazelisk-darwin-arm64
231ec5ca8115e94c75a1f4fbada1a062b48822ca04f21f26e4cb1cd8973cd458  bazelisk-linux-amd64
f9119deb1eeb6d730ee8b2e1a14d09cb45638f0447df23144229c5b3b3bc2408  bazelisk-linux-arm64
0eca0630e072434c63614b009bf5b63a7dff489a8676b560ce63e0d91ab731cd  bazelisk-windows-amd64.exe

[bizrad]

checksums for 1.12.0

0f4873534e49db2fc915c127aca86ec5ece0b4ee9042ee5020835be34682661b  bazelisk-darwin
70cf7fe74808d16418d371feb8ccd4e7c44215db03d2c4ffc75b767b765409fb  bazelisk-darwin-amd64
345bb8b900d6b9ef74234e9e9e413aed38fb29ef255e4ae18ac61bf4a6102d84  bazelisk-darwin-arm64
6b0bcb2ea15bca16fffabe6fda75803440375354c085480fe361d2cbf32501db  bazelisk-linux-amd64
29d861ca48df24a3e8dec57fb00508ba664a31921047b2686c38cf9a20d4639f  bazelisk-linux-arm64
f5ace51c34aaf508e32219a07de768b6f6f92f01993800e853a55dc49d3da89c  bazelisk-windows-amd64.exe