Add rxjs example

[This forum post](https://forum.babylonjs.com/t/rxjs-observable/10438/5) discussed the issue of wrapping BJS Observables into rxjs. There even was an [issue opened](BabylonJS#140), but no PR.

content/features/featuresDeepDive/events/observables.md

@@ -302,3 +302,41 @@ scene.onPointerUp = () => {
     advancedTimer.stop();
 }
 ```
+
+## Usage with RxJS
+
+[RxJS](https://rxjs.dev/) is a common library for handling Observables which are compliant with the [current ECMAScript Observable proposal](https://github.com/tc39/proposal-observable#ecmascript-observable). It provides a wide range of operators, allowing for advanced execution patterns.
+
+The following (TypeScript) code can be used to convert a Babylon Observable into its RxJS equivalent:
+
+```typescript
+/**
+ * Wraps a Babylon Observable into an rxjs Observable
+ * 
+ * @param bjsObservable The Babylon Observable you want to observe
+ * @example
+ * ```
+ * import { Engine, Scene, AbstractMesh } from '@babylonjs/core'
+ *
+ * const canvas = document.getElementById('canvas') as HTMLCanvasElement
+ * const engine = new Engine(canvas)
+ * const scene = new Scene(engine)
+ *
+ * const render$: Observable<Scene> = fromBabylonObservable(scene.onAfterRenderObservable)
+ * const onMeshAdded$: Observable<AbstractMesh> = fromBabylonObservable(scene.onNewMeshAddedObservable)
+ * ```
+ */
+export function fromBabylonObservable<T>(
+  bjsObservable: BJSObservable<T>
+): Observable<T> {
+  return new Observable<T>((subscriber) => {
+    if (!(bjsObservable instanceof BJSObservable)) {
+      throw new TypeError("the object passed in must be a Babylon Observable");
+    }
+
+    const handler = bjsObservable.add((v) => subscriber.next(v));
+
+    return () => bjsObservable.remove(handler);
+  });
+}
+```