[@xstate/store] Readme (#4842)

* Update JS docs

* Add small example

* Move to store-counter-react

* Update example README.md

* Add readme

* Changeset

* ctx -> context

.changeset/perfect-keys-roll.md

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+---
+'@xstate/store': patch
+---
+
+Update README.md

packages/xstate-store/README.md

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 # `@xstate/store`
+
+XState Store is a library for **simple event-based state management**. If you want a state management library that allows you to update a store's state via events, `@xstate/store` is a great option. If you need more complex application logic needs, like state machines/statecharts, effects, communicating actors, and more, consider [using XState instead](https://github.com/statelyai/xstate).
+
+- **Extremely simple**: transitions update state via events, just like Redux, Zustand, Pinia, etc.
+- **Extremely small**: less than 1kb minified/gzipped
+- **XState compatible**: use it with (or without) XState, or convert to XState machines when you need to handle more complex logic & effects.
+- **Extra type-safe**: great typing out of the box, with strong inference and no awkwardness.
+
+> [!NOTE]
+> This readme is written for [TypeScript](#typescript) users. If you are a JavaScript user, just remove the types.
+
+## Installation
+
+```bash
+# yarn add @xstate/store
+# pnpm add @xstate/store
+npm install @xstate/store
+```
+
+## Quick start
+
+```ts
+import { createStore } from '@xstate/store';
+
+// 1. Create a store
+export const donutStore = createStore(
+  {
+    donuts: 0,
+    favoriteFlavor: 'chocolate'
+  },
+  {
+    addDonut: {
+      donuts: (context) => context.donuts + 1
+    },
+    changeFlavor: {
+      favoriteFlavor: (context, event: { flavor: string }) => event.flavor
+    },
+    eatAllDonuts: {
+      donuts: 0
+    }
+  }
+);
+
+console.log(store.getSnapshot());
+// {
+//   status: 'active',
+//   context: {
+//     donuts: 0,
+//     favoriteFlavor: 'chocolate'
+//   }
+// }
+
+// 2. Subscribe to the store
+store.subscribe((snapshot) => {
+  console.log(snapshot.context);
+});
+
+// 3. Send events
+store.send({ type: 'addDonut' });
+// logs { donuts: 1, favoriteFlavor: 'chocolate' }
+
+store.send({
+  type: 'changeFlavor',
+  flavor: 'strawberry' // Strongly-typed!
+});
+// logs { donuts; 1, favoriteFlavor: 'strawberry' }
+```
+
+## Usage with React
+
+Import `useSelector` from `@xstate/store/react`. Select the data you want via `useSelector(…)` and send events using `store.send(eventObject)`:
+
+```tsx
+import { donutStore } from './donutStore.ts';
+import { useSelector } from '@xstate/store/react';
+
+function DonutCounter() {
+  const donutCount = useSelector(donutStore, (state) => state.context.donuts);
+
+  return (
+    <div>
+      <button onClick={() => donutStore.send({ type: 'addDonut' })}>
+        Add donut ({donutCount})
+      </button>
+    </div>
+  );
+}
+```
+
+## Usage with Immer
+
+XState Store makes it really to integrate with immutable update libraries like [Immer](https://github.com/immerjs/immer) or [Mutative](https://github.com/unadlib/mutative). Pass the `produce` function into `createStoreWithProducer(producer, …)`, and update `context` in transition functions using the convenient pseudo-mutative API:
+
+```ts
+import { createStoreWithProducer } from '@xstate/store';
+import { produce } from 'immer'; // or { create } from 'mutative'
+
+const donutStore = createStoreWithProducer(
+  produce,
+  {
+    donuts: 0,
+    favoriteFlavor: 'chocolate'
+  },
+  {
+    addDonut: (context) => {
+      context.donuts++; // "Mutation" (thanks to the producer)
+    },
+    changeFlavor: (context, event: { flavor: string }) => {
+      context.favoriteFlavor = event.flavor;
+    },
+    eatAllDonuts: (context) => {
+      context.donuts = 0;
+    }
+  }
+);
+
+// Everything else is the same!
+```
+
+## TypeScript
+
+XState Store is written in TypeScript and provides full type safety, _without_ you having to specify generic type parameters. The `context` type is inferred from the initial context object, and the event types are inferred from the event object payloads you provide in the transition functions.
+
+```ts
+import { createStore } from '@xstate/store';
+
+const donutStore = createStore(
+  // Inferred as:
+  // {
+  //   donuts: number;
+  //   favoriteFlavor: string;
+  // }
+  {
+    donuts: 0,
+    favoriteFlavor: 'chocolate'
+  },
+  {
+    // Event inferred as:
+    // {
+    //   type: 'changeFlavor';
+    //   flavor: string;
+    // }
+    changeFlavor: (context, event: { flavor: string }) => {
+      context.favoriteFlavor = event.flavor;
+    }
+  }
+);
+
+donutStore.getSnapshot().context.favoriteFlavor; // string
+
+donutStore.send({
+  type: 'changeFlavor', // Strongly-typed from transition key
+  flavor: 'strawberry' // Strongly-typed from { flavor: string }
+});
+```
+
+If you want to make the `context` type more specific, you can strongly type the `context` outside of `createStore(…)` and pass it in:
+
+```ts
+import { createStore } from '@xstate/store';
+
+interface DonutContext {
+  donuts: number;
+  favoriteFlavor: 'chocolate' | 'strawberry' | 'blueberry';
+}
+
+const donutContext: DonutContext = {
+  donuts: 0,
+  favoriteFlavor: 'chocolate'
+};
+
+const donutStore = createStore(donutContext, {
+  // ... (transitions go here)
+});
+```