docs: added voice selection (#193)

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Fixes #<issue_number_goes_here> 🦕

dialogflow-cx/detect-intent-streaming.js

@@ -93,6 +93,13 @@ async function main(
           config: {
             audioEncoding: encoding,
             sampleRateHertz: sampleRateHertz,
+            synthesize_speech_config: {
+              voice: {
+                // Set's the name and gender of the ssml voice
+                name: 'en-GB-Standard-A',
+                ssml_gender: 'SSML_VOICE_GENDER_FEMALE',
+              },
+            },
             singleUtterance: true,
           },
         },