docs(core): 📝 add snapshot doc page

docs/docs/state-snapshot.md

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+---
+sidebar_position: 8
+---
+
+# State Snapshot
+
+The snapshot feature enables you to capture and later restore the state of all stores currently in scope or a selected subset of stores within your application. This can be particularly useful for scenarios where you need to save and later restore application state, such as when performing a rollback or in response to user actions.
+
+This proves specificaly invaluable for providing transactional guarantees for the application state. While the [history plugin](./plugins/history.md) effectively captures the history of one store, a snapshot allows you to **rollback multiple actions across various stores.**
+
+## Usage
+
+A snapshot is a representation of the application state at a specific point in time. It includes a timestamp indicating when the snapshot was created and a `restore` method to revert the application state to the captured snapshot.
+
+### Snapshot Creation
+
+The `createSnapshot` function is used to generate a state snapshot. It accepts a variable number of store instances or store classes as parameters. If no stores are provided, the snapshot will include all stores.
+
+```typescript
+import { createSnapshot } from 'signalstory';
+
+// Capture all stores
+const snapshot1 = createSnapshot();
+
+// You can use the store Class Types
+const snapshot2 = createSnapshot(BookStore, UserStore);
+
+// You can use store instances
+const store1 = new Store<string>({ initialState: '' });
+const store2 = new Store<string>({ initialState: '' });
+const snapshot3 = createSnapshot(store1, store2);
+
+// Or mix
+const snapshot4 = createSnapshot(store1, BookStore);
+```
+
+### Snapshot Restoration
+
+To restore the application state to a specific snapshot, call the `restore` method on the created snapshot. All captured stores will rollback their respective state.
+
+```typescript
+snapshot.restore();
+```