bpftools: add homepage

> This is the official home for bpftool.

pkgs/os-specific/linux/bpftools/default.nix

···
   '';
 
   meta = with lib; {
+    homepage    = "https://github.com/libbpf/bpftool";
     description = "Debugging/program analysis tools for the eBPF subsystem";
     license     = [ licenses.gpl2 licenses.bsd2 ];
     platforms   = platforms.linux;