async.md

This doc describes about the behavior with async.

Some notes

• You need to wrap components with <Suspense> inside <Provider>.
• You can have as many <Suspense> as you need.
• If the read function of an atom returns a promise, the atom will suspend.
• This applies to dependent atoms too.
• If a primitive atom has a promise as the initial value, it will suspend at the first use (when Provider doesn't have it.)
• If the write function of an atom returns a promise, the atom will suspend. There's no way to know as of now if an atom suspends because of read or write.
• You can create a write function so that it works asynchronously, but does not return a promise. In such a case, the atom won't suspend. (This means you can't catch async errors outside. So, you need to catch errors inside write function.)