Add help text

bora.sh

@@ -1,5 +1,11 @@
 #!/usr/bin/sh
 
+if [ $# = 0 ]
+then
+	echo "Usage: $0 <URL> <output>"
+	exit
+fi
+
 webcams=webcams.webm
 deskshare=deskshare.webm
 if [ "$1" != "-" ]