add history

Author: Hao Yuan

src/aks-preview/HISTORY.rst

@@ -11,6 +11,7 @@ To release a new version, please select a new version number (usually plus 1 to
 
 Pending
 +++++++
+* Hide `--enable-managed-system-pool` parameter for `az aks create` for now, as the feature is not ready yet.
 
 18.0.0b43
 +++++++
@@ -43,7 +44,7 @@ Pending
 * Add option `AzureLinuxOSGuard` and `AzureLinux3OSGuard` to `--os-sku` for `az aks nodepool add` and `az aks nodepool update`.
 * Add machine command `az aks machine add` to add a machine to an existing machine pool.
 * Add blue-green upgrade strategy support for AKS node pools:
-  - `az aks nodepool add/update/upgrade`: Add `--upgrade-strategy` parameter to switch between rolling and blue-green nodepool upgrades. 
+  - `az aks nodepool add/update/upgrade`: Add `--upgrade-strategy` parameter to switch between rolling and blue-green nodepool upgrades.
   - `az aks nodepool add/update/upgrade`: Add `--drain-batch-size`, `--drain-timeout-bg`, `--batch-soak-duration`, `--final-soak-duration` parameters to configure blue-green upgrade settings.
 
 18.0.0b38