(docs) Document Server Actions .bind method

[shuding]

This will be the recommended way of passing extra arguments to a Server Action. A couple of reasons behind:

• This is better than putting a hidden <input hidden value={userId}/> because that will appear in the SSR'd HTML as full text and cannot be encoded. With .bind, we can handle that in the future.
• This is better than event callbacks onSubmit={(e) => { await updateUser(userId, e.target.formData) }} as this supports progressive enhancement.
• This is better than re-creating a new action action={async (formData) => { "use server"; return updateUser(userId, formData) }} as inlined "use server" only works in Server Components.