Merged PR 6783: Added warning about custom shell leading to undeployable image

Added warning about custom shell leading to undeployable image - per request from partners, dev, and PMs.

@<Jeanie Decker> - can you take a look? I can forward you the thread that led to this request, if needed. Here's part of the thread, from Michael Niehaus:
The “hide shell” setup is really just a “RunOnce” entry that never really finishes – it might reboot the machine and run again, and eventually runs out of commands to process so at that point it exits.  So that is still using Explorer.exe as John said.

There was a question on EShell.exe too:  I believe that’s a creation of the Embedded team (I believe Suma has some background) that was later integrated into standard Windows SKUs.

Back to John’s question though:

is it fair to make the statement that setting a custom shell prior to OOBE won’t result in a deployable image?  That’s been true for a couple of releases now, and I don’t think that necessarily directly impacts the scenarios that Michael has highlighted as uses of custom shell, but I want to confirm.

Thanks,
-Michael

windows/configuration/setup-kiosk-digital-signage.md

@@ -8,7 +8,7 @@ ms.mktglfcycl: manage
 ms.sitesec: library
 author: jdeckerms
 ms.localizationpriority: high
-ms.date: 03/23/2018
+ms.date: 03/30/2018
 ---
 
 # Set up a kiosk or digital signage on Windows 10 Pro, Enterprise, or Education
@@ -284,7 +284,8 @@ Using Shell Launcher, you can configure a kiosk device that runs a Classic Windo
 >You can also configure a kiosk device that runs a Classic Windows application by using the [Provision kiosk devices wizard](#wizard).
 
 >[!WARNING]
->Shell Launcher doesn't support a custom shell with an application that launches a different process and exits. For example, you cannot specify **write.exe** in Shell Launcher. Shell Launcher launches a custom shell and monitors the process to identify when the custom shell exits. **Write.exe** creates a 32-bit wordpad.exe process and exits. Because Shell Launcher is not aware of the newly created wordpad.exe process, Shell Launcher will take action based on the exit code of **Write.exe**, such as restarting the custom shell.  
+>- Windows 10 doesn’t support setting a custom shell prior to OOBE. If you do, you won’t be able to deploy the resulting image.
+>- Shell Launcher doesn't support a custom shell with an application that launches a different process and exits. For example, you cannot specify **write.exe** in Shell Launcher. Shell Launcher launches a custom shell and monitors the process to identify when the custom shell exits. **Write.exe** creates a 32-bit wordpad.exe process and exits. Because Shell Launcher is not aware of the newly created wordpad.exe process, Shell Launcher will take action based on the exit code of **Write.exe**, such as restarting the custom shell.  
 
 ### Requirements
 

windows/configuration/wcd/wcd-smisettings.md

@@ -7,7 +7,7 @@ ms.sitesec: library
 author: jdeckerMS
 ms.localizationpriority: medium
 ms.author: jdecker
-ms.date: 09/06/2017
+ms.date: 03/30/2018
 ---
 
 # SMISettings (Windows Configuration Designer reference)
@@ -94,6 +94,9 @@ When you **enable** KeyboardFilter, a number of other settings become available
 
 Use ShellLauncher to specify the application or executable to use as the default custom shell. One use of ShellLauncher is to [create a kiosk (fixed-purpose) device running a Classic Windows application](https://docs.microsoft.com/windows/configuration/set-up-a-kiosk-for-windows-10-for-desktop-editions#shell-launcher-for-classic-windows-applications).
 
+>[!WARNING]
+>Windows 10 doesn’t support setting a custom shell prior to OOBE. If you do, you won’t be able to deploy the resulting image.
+
 You can also configure ShellLauncher to launch different shell applications for different users or user groups.
 
 >[!IMPORTANT]