docs: add a notice about the compatibility of Ingress and Dashboard (#319)

Signed-off-by: Ling Samuel <lingsamuelgrace@gmail.com>
diff --git a/README.md b/README.md
index f2ccb2f..663bded 100644
--- a/README.md
+++ b/README.md
@@ -24,3 +24,5 @@
 - [Apache APISIX Helm Chart](./docs/en/latest/apisix.md)
 - [Apache APISIX Dashboard Helm Chart](./docs/en/latest/apisix-dashboard.md)
 - [Apache APISIX Ingress Controller Helm Chart](./docs/en/latest/apisix-ingress-controller.md)
+
+Currently, APISIX Ingress Controller automatically manipulates some APISIX resources, which is not very compatible with APISIX Dashboard. In addition, users should not modify resources labeled `managed-by: apisix-ingress-controllers` via APISIX Dashboard.