Add comments on the instructions

[ale-grassi]

Enums used for convenience have shortened names, so sometimes their meaning is not immediate; it might be useful to clarify their meaning.

Documentation of the various instructions can be found here

pub(crate) enum ArmModeAluInstruction {
    And = 0x0,  // AND logical
    Eor = 0x1,  // XOR logical
    ...
    Bic = 0xE,  // Bit clear
}

The same applies to the Condition enum.

It would also be useful to discuss whether or not it is worthwhile to write down not only what they mean, but also how they work. For example, in addition to writing that bic = bit clear, it might be useful to explain that it does: Rd = Rn AND NOT Op2