update reademe and upgrade notice

NoticeOnUpgradeTov9.0.md

@@ -0,0 +1,9 @@
+# Notice on Upgrade to v9.x
+
+## New default value for variable `agents_pool_max_surge`
+
+variable `agents_pool_max_surge` now has default value `10%`. This change might cause configuration drift. If you want to keep the old value, please set it explicitly in your configuration.
+
+## API version for `azapi_update_resource` resource has been upgraded from `Microsoft.ContainerService/managedClusters@2023-01-02-preview` to `Microsoft.ContainerService/managedClusters@2024-02-01`.
+
+After a test, it won't affect the existing Terraform state and cause configuration drift. The upgrade is caused by the retirement of original API.

README.md

@@ -14,6 +14,7 @@ In most cases, you will need to adjust your Terraform code to accommodate the ch
 
 To help you in this process, we have provided detailed documentation on the breaking changes, new features, and any deprecated functionalities. Please take the time to read through these resources to avoid any potential issues or disruptions to your infrastructure.
 
+* [Notice on Upgrade to v9.x](./NoticeOnUpgradeTov9.0.md)
 * [Notice on Upgrade to v8.x](./NoticeOnUpgradeTov8.0.md)
 * [Notice on Upgrade to v7.x](./NoticeOnUpgradeTov7.0.md)
 * [Notice on Upgrade to v6.x](./NoticeOnUpgradeTov6.0.md)