[Docs] Improve `atomFamily` typings to be obvious to use

As per https://github.com/pmndrs/jotai/discussions/433#discussion-3327022

It’s not currently 100% correct how atomFamily typings are working now especially if you want to explicitly pass generic arguments to it.

For instance:

export const profitLossEngineAtom = atomFamily<
  ProfitLossFamilyInitialize,
  ProfitLossEngineState,
  SetStateAction<ProfitLossEngineState>
>(
  ({ id }) => {
    const anAtom = atom({ id, queries: {}, queryResult: {} });
    anAtom.onMount = (setAtom) => {
      setAtom({ id, queries: {}, queryResult: {} });
    };
    return anAtom;
  },
  (a, b) => a.id === b.id
);

If you pass third argument to be just ProfitLossEngineState it will break typings for all the setters that would like to use a callback like setAtomState(it => ({ ...it, queries: { ... }})) It’s a bit counterintuitive especially since it used to work just fine before.

To understand the problem better and get reproduces etc. read the discussion above.

[dai-shi]

@HosseinAgha Thanks for chiming in. I will add some notes in docs.

[dai-shi]

https://github.com/pmndrs/website/pull/65#issuecomment-830792790