update audio content creation url in hub

Author: Rob Chambers

articles/cognitive-services/Speech-Service/index.md

@@ -744,7 +744,7 @@ description: Get started with the Speech service.
                                 </a>
                             </li>
                             <li>
-                                <a href="https://aka.ms/speech/custom-tts-overview">
+                                <a href="https://aka.ms/speech/custom-tts-content">
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