New comment by Piraty on void-packages repository

https://github.com/void-linux/void-packages/pull/31614#issuecomment-866168047

Comment:
from Manual.md

```
If a distfile changes its checksum for every download because it is packaged
on the fly on the server, like e.g. snapshot tarballs from any of the
`https://*.googlesource.com/` sites, the checksum of the `archive contents`
can be specified by prepending a commercial at (@).
For tarballs you can find the contents checksum by using the command
`tar xf <tarball.ext> --to-stdout | sha256sum`.
```