termux-tts-engines: Add -h support and validate

packages/termux-api/termux-tts-engines

@@ -1,3 +1,24 @@
 #!/bin/sh
+set -e -u
+
+SCRIPTNAME=termux-tts-engines
+show_usage () {
+	echo "Usage: $SCRIPTNAME"
+	echo "Get information about the available text-to-speech (TTS) engines."
+	echo ""
+	echo "The name of an engine may be given to the termux-tts-speak command using the -e option."
+	exit 0
+}
+
+while getopts :h option
+do
+    case "$option" in
+	h) show_usage;;
+	?) echo "$SCRIPTNAME: illegal option -$OPTARG"; exit 1;
+    esac
+done
+shift $(($OPTIND-1))
+
+if [ $# != 0 ]; then echo "$SCRIPTNAME: too many arguments"; exit 1; fi
 
 @TERMUX_API@ TextToSpeech --es engine LIST_AVAILABLE