Update docs with availability zone preview notes

website/docs/d/managed_disk.html.markdown

@@ -111,4 +111,6 @@ resource "azurerm_virtual_machine" "test" {
 * `os_type` - The operating system for managed disk. Valid values are `Linux` or `Windows`
 * `disk_size_gb` - The size of the managed disk in gigabytes.
 * `tags` - A mapping of tags assigned to the resource.
-* `zones` - (Optional) A collection containing the availability zone the managed disk is allocated in.
+* `zones` - (Optional) A collection containing the availability zone the managed disk is allocated in.
+
+-> **Please Note**: Availability Zones are [in Preview and only supported in several regions at this time](https://docs.microsoft.com/en-us/azure/availability-zones/az-overview) - as such you must be opted into the Preview to use this functionality. You can [opt into the Availability Zones Preview in the Azure Portal](http://aka.ms/azenroll).

website/docs/r/loadbalancer.html.markdown

@@ -60,6 +60,8 @@ The following arguments are supported:
 * `public_ip_address_id` - (Optional) Reference to Public IP address to be associated with the Load Balancer.
 * `zones` - (Optional) A collection containing the availability zone to allocate the IP in.
 
+-> **Please Note**: Availability Zones are [in Preview and only supported in several regions at this time](https://docs.microsoft.com/en-us/azure/availability-zones/az-overview) - as such you must be opted into the Preview to use this functionality. You can [opt into the Availability Zones Preview in the Azure Portal](http://aka.ms/azenroll).
+
 ## Attributes Reference
 
 The following attributes are exported:

website/docs/r/managed_disk.html.markdown

@@ -108,6 +108,8 @@ The following arguments are supported:
 
 * `zones` - (Optional) A collection containing the availability zone to allocate the Managed Disk in.
 
+-> **Please Note**: Availability Zones are [in Preview and only supported in several regions at this time](https://docs.microsoft.com/en-us/azure/availability-zones/az-overview) - as such you must be opted into the Preview to use this functionality. You can [opt into the Availability Zones Preview in the Azure Portal](http://aka.ms/azenroll).
+
 For more information on managed disks, such as sizing options and pricing, please check out the
 [azure documentation](https://docs.microsoft.com/en-us/azure/storage/storage-managed-disks-overview).
 

website/docs/r/public_ip.html.markdown

@@ -62,6 +62,8 @@ The following arguments are supported:
 
 * `zones` - (Optional) A collection containing the availability zone to allocate the Public IP in.
 
+-> **Please Note**: Availability Zones are [in Preview and only supported in several regions at this time](https://docs.microsoft.com/en-us/azure/availability-zones/az-overview) - as such you must be opted into the Preview to use this functionality. You can [opt into the Availability Zones Preview in the Azure Portal](http://aka.ms/azenroll).
+
 ## Attributes Reference
 
 The following attributes are exported:

website/docs/r/virtual_machine.html.markdown

@@ -248,6 +248,8 @@ The following arguments are supported:
 * `tags` - (Optional) A mapping of tags to assign to the resource.
 * `zones` - (Optional) A collection containing the availability zone to allocate the Virtual Machine in.
 
+-> **Please Note**: Availability Zones are [in Preview and only supported in several regions at this time](https://docs.microsoft.com/en-us/azure/availability-zones/az-overview) - as such you must be opted into the Preview to use this functionality. You can [opt into the Availability Zones Preview in the Azure Portal](http://aka.ms/azenroll).
+
 For more information on the different example configurations, please check out the [azure documentation](https://msdn.microsoft.com/en-us/library/mt163591.aspx#Anchor_2)
 
 `Plan` supports the following:

website/docs/r/virtual_machine_scale_set.html.markdown

@@ -262,6 +262,8 @@ The following arguments are supported:
 * `tags` - (Optional) A mapping of tags to assign to the resource.
 * `zones` - (Optional) A collection of availability zones to spread the Virtual Machines over.
 
+-> **Please Note**: Availability Zones are [in Preview and only supported in several regions at this time](https://docs.microsoft.com/en-us/azure/availability-zones/az-overview) - as such you must be opted into the Preview to use this functionality. You can [opt into the Availability Zones Preview in the Azure Portal](http://aka.ms/azenroll).
+
 `sku` supports the following:
 
 * `name` - (Required) Specifies the size of virtual machines in a scale set.