Update README.md

README.md

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-# TextToSpeechListener
+# TextToSpeechListener
+
+The text-to-speech listener (TTSL) is a C# console app. It will listen for data transferred via a UDP socket.
+The incoming data is expected to be in JSON format. The contained text will be synthesized to speech via the Microsoft or Google TTS engines.
+
+The common use case is that another program (or game) sends the text data via the UDP protocol. The listener receives the data and converts it into speech.
+
+Note that this program is closely related to Ciribob's DCS-External-Audio program but it does not use any radio frequencies or SRS running.
+One major advantage is, that the listener console app is constantly running. There is no "pop-up" window, each time a TTS package is received.
+
+NOTE:
+* For google you have to set the Windows environment variable `GOOGLE_APPLICATION_CREDENTIALS` to point to google crendentials file.
+* The default UDP port of the listener is 11042. But it can be configured to use any other port. 
+* The TTS messages are played synchronously, *i.e.* they are played one after the other and do not overlap each other.
+
+![image](https://user-images.githubusercontent.com/28947887/234686638-79272a70-aaff-426d-9d01-6252bf779a1b.png)