Update OneCore voices URL and instructions (PR #11993)

The existing URL in the user guide with the list of OneCore voices languages and installation instructions was out of date.

- Added overview of how to install new voices
- Added updated link to list of available languages / voices

user_docs/en/userGuide.t2t

@@ -2253,7 +2253,17 @@ Windows 10 includes new voices known as "OneCore" or "mobile" voices.
 Voices are provided for many languages, and they are more responsive than the Microsoft voices available using Microsoft Speech API version 5.
 On Windows 10, NVDA uses Windows OneCore voices by default ([eSpeak NG #eSpeakNG] is used in other releases).
 
-Please see this Microsoft article for a list of available voices and instructions to install them: https://support.microsoft.com/en-us/help/22797/windows-10-narrator-tts-voices
+To add new Windows OneCore voices, go to "Speech Settings", within Windows system settings. 
+Use the "Add voices" option and search for the desired language.
+Many languages include multiple variants.
+"United Kingdom" and "Australia" are two of the English variants.
+"France", "Canada" and "Switzerland" are French variants available.
+Search for the broader language (such as English or French), then locate the variant in the list.
+Select any languages desired and use the "add" button to add them.
+Once added, restart NVDA.
+
+
+Please see this Microsoft article for a list of available voices: https://support.microsoft.com/en-us/windows/appendix-a-supported-languages-and-voices-4486e345-7730-53da-fcfe-55cc64300f01
 
 + Supported Braille Displays +[SupportedBrailleDisplays]
 This section contains information about the Braille displays supported by NVDA.