feat: first argument to writable could be optional

site/content/docs/03-run-time.md

@@ -245,10 +245,10 @@ This makes it possible to wrap almost any other reactive state handling library
 #### `writable`
 
 ```js
-store = writable(value: any)
+store = writable(value?: any)
 ```
 ```js
-store = writable(value: any, (set: (value: any) => void) => () => void)
+store = writable(value?: any, start?: (set: (value: any) => void) => () => void)
 ```
 
 ---

src/runtime/store/index.ts

@@ -61,7 +61,7 @@ export function readable<T>(value: T, start: StartStopNotifier<T>): Readable<T>
  * @param {*=}value initial value
  * @param {StartStopNotifier=}start start and stop notifications for subscriptions
  */
-export function writable<T>(value: T, start: StartStopNotifier<T> = noop): Writable<T> {
+export function writable<T>(value?: T, start: StartStopNotifier<T> = noop): Writable<T> {
 	let stop: Unsubscriber;
 	const subscribers: Array<SubscribeInvalidateTuple<T>> = [];