Add syscall compatibility table to proot

[deliciouslytyped]

New system calls get added to linux eventually, it would be good to have a visible resource the explains proot's support for syscalls at any given time. This would also be easier to update than actually adding any given syscall, so users would have a place to check if something doesn't work.

It has been brought to my attention that proot-rs has a table, but it's not immediately clear if this has anything to do with normal proot; https://github.com/proot-me/proot-rs/wiki/Translation-of-system-calls

[oxr463]

Reference(s):

• https://man7.org/linux/man-pages/man2/syscalls.2.html