kbfs: update homepage and description

(cherry picked from commit d8bbbeb38a6dd5e1fca88a4196b1a848e1c6dd3d)

pkgs/tools/security/keybase/kbfs.nix

···
   buildFlags = [ "-tags production" ];
 
   meta = with stdenv.lib; {
-    homepage = https://www.keybase.io;
-    description = "The Keybase FS FUSE driver";
+    homepage = "https://keybase.io/docs/kbfs";
+    description = "The Keybase filesystem";
     platforms = platforms.unix;
     maintainers = with maintainers; [ rvolosatovs bennofs np ];
     license = licenses.bsd3;