Update Set-SPOSiteDesign.md

Added required parameter -Identity.

Author: aaronmi

sharepoint/sharepoint-ps/sharepoint-online/Set-SPOSiteDesign.md

@@ -15,6 +15,7 @@ Updates a previously uploaded site design.
 
 ```powershell
 Set-SPOSiteDesign
+  [-Identity <SPOSiteDesignPipeBind>]
   [-Title <string>]
   [-WebTemplate <string>]
   [-SiteScripts <SPOSiteScriptPipeBind[]>]
@@ -46,6 +47,21 @@ Updates a previously uploaded site design.
 
 ## PARAMETERS
 
+### -Identity
+The site design Id.
+
+```yaml
+Type: SPOSiteDesignPipeBind
+Parameter Sets: (All)
+Aliases: 
+Applicable: SharePoint Online
+Required: True
+Position: Named
+Default value: None
+Accept pipeline input: False
+Accept wildcard characters: False 
+```
+
 ### -Title
 The display name of the site design.