termux-tts-speak: Replace incorrect 'device-tts-engines' with 'termux-tts-engines'

packages/termux-api/termux-tts-speak

@@ -4,12 +4,11 @@ set -u
 
 PARAMS=""
 
-SCRIPTNAME=$0
 show_usage () {
-	echo "usage: $SCRIPTNAME [OPTIONS]"
+	echo "usage: termux-tts-speak [OPTIONS]"
 	echo ""
-	echo "Speak with a device text-to-speech (TTS) engine."
-	echo "Find out about valid options with the device-tts-engines program."
+	echo "Speak stdin input with a system text-to-speech (TTS) engine."
+	echo "Find out about available engines by executing 'termux-tts-engines'."
 	echo "  -e, --engine <engine>        TTS engine to use"
 	echo "  -l, --language <language>    language to speak in (may be unsupported by the engine)"
 	echo "  -p, --pitch <pitch>          pitch to use in speech"