Add checksum for the releases

[pevik]

Could you please add checksum for releases? Ideally at least sha256. It helps both users and Linux distros to verify tarballs before compiling.

[pevik]

Thank you.

[radioactiveman]

You are welcome.

In addition I have created sha256 files for all Audacious 4.x tarballs at https://distfiles.audacious-media-player.org/.