[docs] A suggestion to change decimal module docstring

Not worth a tracker entry, so I am just sending this to docs and Mark. I find current "(for instance, in binary floating point, 1.00 % 0.1 gives 0.09999999999999995 instead of the expected Decimal("0.00") returned by decimal floating point)" in the introduction a bit unclear because neither Decimal class nor it's constructor taking a string has been introduced by that point. I think it is better to just use 0.00 for the "expected" value.