Docs: comment acr.kubevela.net as deprecated (#1301)

see: kubevela/velaux#879

Signed-off-by: William Wang <[email protected]>

docs/reference/addons/velaux.md

@@ -286,9 +286,9 @@ By default the image repo is docker hub, you can specify the image repo by the `
 vela addon enable velaux repo=acr.kubevela.net
 ```
 
-You can try to specify the `acr.kubevela.net` image registry as an alternative, It's maintained by KubeVela team, and we will upload/sync the built-in addon image for convenience.
+Please note that `acr.kubevela.net` is **no longer maintained** and documented here just for example, in case you use `repo=your-registry.com`, the image to deploy velaux server will be `your-registry.com/oamdev/velaux:<velaux-version>`.
 
-This feature can also help you to build your private installation, just upload all images to your private image registry.
+This feature can help you to build your private installation, just upload all images to your private image registry.
 
 ## Concept of VelaUX