Documentation omission: Compound modulo is not mentioned

[nickgammon]

On the main reference page https://www.arduino.cc/en/Reference/HomePage there are some compound operators (eg. += ).

However compound modulo is omitted.

%= (compound modulo)

I suggest adding it.

[agdl]

@nickgammon added in the same page of the other. If it is ok for you close the issue please!