docs: move the voice list examples to the man files.

docs/voices.md

 Voice files are placed in the `espeak-data/voices` directory,
 or within subdirectories in there.
 
-The available voice files can be listed by:
-
-	espeak-ng --voices
-
-or
-
-	espeak-ng --voices=<language>
-
-also
-
-	espeak-ng --voices=<variant>
-
-Lists voice variants which can be applied to eSpeak NG voices.
-
-	espeak-ng --voices=<mbrola>
-
-Lists the Mbrola voices.
-
 ## Contents of Voice Files
 
 The `language` attribute is mandatory. All the other attributes are

src/espeak-ng.1.ronn

   * `espeak-ng -ven-us "[[h@'loU]]"`:
     Speak the phonemes "h@'loU" using the American English voice.
 
+  * `espeak-ng --voices`:
+    List all voices supported by eSpeak.
+
+  * `espeak-ng --voices=en`:
+    List all voices that speak English (`en`).
+
+  * `espeak-ng --voices=mb`:
+    List all voices using the MBROLA voice synthesizer.
+
 ## AUTHOR
 
 eSpeak NG is maintained by Reece H. Dunn <[email protected]>. It is based on

src/speak-ng.1.ronn

   * `speak-ng -ven-us "[[h@'loU]]"`:
     Speak the phonemes "h@'loU" using the American English voice.
 
+  * `speak-ng --voices`:
+    List all voices supported by eSpeak.
+
+  * `speak-ng --voices=en`:
+    List all voices that speak English (`en`).
+
+  * `speak-ng --voices=mb`:
+    List all voices using the MBROLA voice synthesizer.
+
 ## AUTHOR
 
 eSpeak NG is maintained by Reece H. Dunn <[email protected]>. It is based on