adding_system_call.txt

1)kernel/syscall.c in line 107:
extern uint64 sys_newsyscall(void);

2)kernel/syscall.h in line 23:
#define SYS_newsyscall 22

3)kernel/syscall.c add this after line 130 
inside the curly brackets of the struct:
[SYS_newsyscall] sys_newsyscall,

4)kernel/sysproc.c from line 100 to 105:
uint64
sys_newsyscall(void)
{
// from here you can call other function in the kernel
// from proc.c or trap.c and many others places
return 0;
}

5)user/user.h in line 26:
int newsyscall(void);

6)user/usys.pl in line 39:
entry("newsyscall");