Add readme for arrow function returns

[ylvaselling]

Lmk if you agree

[WeirdRubberDuck]

Just realized: Do we want to make an exception for things like onClick functions on components? In those cases, it is already quite clear that there is not value being retuned, I guess, and adding the extra lines makes the rendered component harder to overview (at least in my opinion)

For example:

  if (visibility === 'Fading') {
    return (
      <ActionIcon onClick={() => updateValue(!checked, isImmediate)}>
        <FadeIcon  />
      </ActionIcon>
    );
  }

compared to:

  if (visibility === 'Fading') {
    return (
      <ActionIcon
        onClick={() => {
          updateValue(!checked, isImmediate);
        }}
      >
        <FadeIcon />
      </ActionIcon>
    );
  }

In this case, I'm not a fan of the extra clutter that the {} and ; add, but that's only my personal opinion

@ylvaselling @engbergandreas @alexanderbock