I am not a Go user so I can't speak about Go specifically, but I feel like including the name of the language in the library name is in general an anti-pattern, since generally when you look for a library to do something in language A, you aren't going to get results using language B anyway.
IMO name should make it clear it is Go-only. Something like "GoastArgs: a Go library that parses a usage string/CLI args into an AST"