Typo in syscalls help

[pacalet]

The Syscalls tab of Help/RISCV provides an example of use of PrintInt:

    li  a7, 1          # service 1 is print integer
    add a0, t0, zero   # load desired value into argument register a0, using pseudo-op
    ecall

The comment of the add a0, t0, zero instruction is erroneous: this is not a pseudo-op, it is a basic instruction.

[privat]

mv a0, t0 is better anyway.

TODO fix src/help/SyscallHelpPrelude.html