Add zstd files to Archives.gitignore

[zengxs]

Reasons for making this change:

Zstandard usage is becoming more widespread, necessitating its inclusion in Archives.gitignore.

Links to documentation supporting these rule changes:

https://en.wikipedia.org/wiki/Tar_(computing)#Suffixes_for_compressed_files

If this is a new template:

• Link to application or project’s homepage: TODO