feat(docs): migrate bs docs

blocksuite/docs-site/guide/slot.md

@@ -0,0 +1,42 @@
+# Slot
+
+BlockSuite extensively uses `Slot` to manage events that are not DOM-native. You can think of it as a type-safe event emitter or a simplified RxJS [Observable](https://rxjs.dev/guide/observable):
+
+```ts
+import { Slot } from '@blocksuite/store';
+
+// Create a new slot
+const slot = new Slot<{ name: string }>();
+
+// Subscribe events
+slot.on(({ name }) => console.log(name));
+
+// Or alternatively only listen event once
+slot.once(({ name }) => console.log(name));
+
+// Emit the event
+slot.emit({ name: 'foo' });
+```
+
+To unsubscribe from the slot, simply use the return value of `slot.on()`:
+
+```ts
+const slot = new Slot();
+const disposable = slot.on(myHandler);
+
+// Dispose the subscription
+disposable.dispose();
+```
+
+Moreover, for any node in the block tree, events can be triggered when the node is updated:
+
+```ts
+const model = doc.root[0];
+
+// Triggered when the `props` of the block model is updated
+model.propsUpdated.on(() => updateMyComponent());
+// Triggered when the `children` of the block model is updated
+model.childrenUpdated.on(() => updateMyComponent());
+```
+
+In the prebuilt AFFiNE editor, which is based on the [lit](https://lit.dev/) framework, the UI component of each block subscribes to its model updates using this pattern.