[llvm-ranlib] Support more than one input file

BSD and GNU ranlib support more than one input file. Implement this.

While here, update OVERVIEW (Ranlib => ranlib) since "ranlib" is more common.
Remove "speed access" since the index has nothing to do with performance: it is
mandatory for GNU ld and gold but ignored for ld.lld (D119074).

Close https://github.com/llvm/llvm-project/issues/54565

Differential Revision: https://reviews.llvm.org/D131375