Document ARM64 Linux bundles in README and release notes

## Summary Follow-up to rstudio/tinytex#483 which added ARM64 Linux builds to the daily workflow. - Update README prose and download table to document the new `-arm64.tar.gz` bundles, with direct download links to the daily release assets - Update monthly release notes template to mention ARM64 bundles The ARM64 bundles currently don't have `yihui.org/tinytex/` redirect URLs, so the table links directly to the GitHub release download URLs.