Add zstd (.zst) to the --search-zip support (extension of #539)

[cemeyer]

What version of ripgrep are you using?

git master

Describe your question, feature request, or bug.

Just need an additional list entry in https://github.com/BurntSushi/ripgrep/blob/master/grep-cli/src/decompress.rs#L349 and a small update to the manual page. Kudos to @balajisivaraman for already having done the work to easily add more decompressors in a general fashion.

Something like:

+ const ARGS_ZSTD: &[&str] = &["zstd", "-d", "-c"];
...
+     cmd("*.zst", ARGS_ZSTD),

I can't find where the OPTIONS (-z, --search-zip) portion of the manual page is stored in the directory hierarchy, but that should be updated as well.

Should be pretty trivial! Thanks for considering it.

[cemeyer]

Awesome, thanks!