add warning note that NLS eReader Zoomax is not supported (#16628)

Related to #15863

Summary of the issue:
The NLS eReader Zoomax is not supported by NVDA currently, despite a message in the user guide suggesting the contrary.
See #15863 for discussion on adding support for the eReader

Description of user facing changes
add warning note that NLS eReader Zoomax is not supported

user_docs/en/userGuide.md

@@ -4035,6 +4035,7 @@ The following extra devices are also supported (and do not require any special d
 * APH Chameleon 20
 * Humanware BrailleOne
 * NLS eReader
+  * Note that the Zoomax is currently not supported without external drivers
 
 Following are the key assignments for  the Brailliant BI/B and BrailleNote touch displays with NVDA.
 Please see the display's documentation for descriptions of where these keys can be found.