Record platform limitation of the Kopia block mode uploader in docs.

Signed-off-by: Xun Jiang <jxun@vmware.com>

design/volume-snapshot-data-movement/volume-snapshot-data-movement.md

@@ -666,6 +666,9 @@ At present, VBDM doesn't support recovery, so it will follow the second rule.
 ## Kopia For Block Device
 To work with block devices, VGDP will be updated. Today, when Kopia attempts to create a snapshot of the block device, it will error because kopia does not support this file type. Kopia does have a nice set of interfaces that are able to be extended though.
 
+**Notice**
+The Kopia block mode uploader only supports non-Windows platforms, because the block mode code invokes some system calls that are not present in the Windows platform.
+
 To achieve the necessary information to determine the type of volume that is being used, we will need to pass in the volume mode in provider interface.
 
 ```go

site/content/docs/main/csi-snapshot-data-movement.md

@@ -248,6 +248,7 @@ that anyone who has access to your backup storage can decrypt your backup data**
 to the backup storage appropriately. 
 - [Velero built-in data mover] Even though the backup data could be incrementally preserved, for a single file data, Velero built-in data mover leverages on deduplication to find the difference to be saved. This means that large files (such as ones storing a database) will take a long time to scan for data  deduplication, even if the actual difference is small.
 - [Velero built-in data mover] You may need to [customize the resource limits][11] to make sure backups complete successfully for massive small files or large backup size cases, for more details refer to [Velero file system level backup performance guide][12]. 
+- The block mode is supported by the Kopia uploader, but it only supports non-Windows platforms, because the block mode code invokes some system calls that are not present in the Windows platform.
 
 ## Troubleshooting
 

site/content/docs/v1.12/csi-snapshot-data-movement.md

@@ -261,6 +261,7 @@ that anyone who has access to your backup storage can decrypt your backup data**
 to the backup storage appropriately. 
 - [Velero built-in data mover] Even though the backup data could be incrementally preserved, for a single file data, Velero built-in data mover leverages on deduplication to find the difference to be saved. This means that large files (such as ones storing a database) will take a long time to scan for data  deduplication, even if the actual difference is small.
 - [Velero built-in data mover] You may need to [customize the resource limits][11] to make sure backups complete successfully for massive small files or large backup size cases, for more details refer to [Velero file system level backup performance guide][12]. 
+- The block mode is supported by the Kopia uploader, but it only supports non-Windows platforms, because the block mode code invokes some system calls that are not present in the Windows platform.
 
 ## Troubleshooting