Add faq

Signed-off-by: pigletfly <wangbing.adam@gmail.com>

docs/frequently-asked-questions.md

@@ -20,3 +20,21 @@ to keep a consistent user experience and behavior.
 
 It's worth noting that not all controllers are needed by Karmada, for the recommended controllers please
 refer to [Recommended Controllers](./userguide/configure-controllers.md#recommended-controllers).
+
+
+## Can I install Karmada in a Kubernetes cluster and reuse the kube-apiserver as Karmada apiserver?
+
+The quick answer is `yes`. In that case, you can save the effort to deploy
+[karmada-apiserver](https://github.com/karmada-io/karmada/blob/master/artifacts/deploy/karmada-apiserver.yaml) and just
+share the APIServer between Kubernetes and Karmada. In addition, the high availability capabilities in the origin clusters
+can be inherited seamlessly. We do have some users using Karmada in this way.
+
+There are some things you should consider before doing so:
+
+- This approach hasn't been fully tested by the Karmada community and no plan for it yet.
+- This approach will increase computation costs for the Karmada system. E.g.
+  After you apply a `resource template`, take `Deployment` as an example, the `kube-controller` will create `Pods` for the
+  Deployment and update the status persistently, Karmada system will reconcile these changes too, so there might be 
+  conflicts.
+
+TODO: Link to adoption use case once it gets on board.