Typo in syscalls help of RARS 1.6

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.