Inconsistent configuration options between README and source code.

[RussellWang9]

As described In README, some configuration options are provided via /sys/kernel/debug/hermit. However, some options do not exist in source code (e.g., no /sys/kernel/debug/hermit/swap_thread and /sys/kernel/debug/hermit/prefetch_thread in source code).

[ivanium]

Hi @wzx-ipads,

Thank you for your interest in Hermit. Those configuration knobs are outdated and removed from the source code. They were exposed experimentally for debug usage and have no performance impact on the current codebase.

Thank you for pointing out the REAMDE inconsistency issue; I will get it fixed soon :)