PublishIISAssets must be set to publish custom web.config (#20243)

Author: pranavkm

aspnetcore/blazor/host-and-deploy/webassembly.md

@@ -434,7 +434,13 @@ When a Blazor project is published, a `web.config` file is created with the foll
 
 #### Use a custom web.config
 
-To use a custom `web.config` file, place the custom `web.config` file at the root of the project folder and publish the project.
+To use a custom `web.config` file, place the custom `web.config` file at the root of the project folder. Configure the project to publish IIS-specific assets using `PublishIISAssets` in the app's project file and publish the project:
+
+```xml
+<PropertyGroup>
+  <PublishIISAssets>true</PublishIISAssets>
+</PropertyGroup>
+```
 
 #### Install the URL Rewrite Module