fix(xtask): libos模式运行需指定zcore的libos feature

[whfuyn]

按照readme里跑libos模式运行的时候报错，提示找不到依赖：

$ cargo linux-libos --args /bin/busybox

error[E0433]: failed to resolve: use of undeclared crate or module `x2apic`
  --> kernel-hal/src/bare/arch/x86_64/drivers.rs:36:9
   |
36 |     use x2apic::lapic::{TimerDivide, TimerMode};
   |         ^^^^^^ use of undeclared crate or module `x2apic`

error[E0433]: failed to resolve: use of undeclared crate or module `uefi`
 --> kernel-hal/src/bare/arch/x86_64/config.rs:3:5
  |
3 | use uefi::proto::console::gop::ModeInfo;
  |     ^^^^ use of undeclared crate or module `uefi`

看了一下发现是因为没有给zcore的feature里指定libos，加了以后运行正常。

顺便在文档里说明了一下如何给busybox传参数。