Update error handlers

convert-psp

@@ -5,11 +5,19 @@ f_convert-psp(){
 }
 
 help(){
-	printf "Usage: $0 \"directory\" \"URL\"\n"
+	printf "Usage: $0\n"
+	exit 1
+}
+
+nojson(){
+	printf "This program needs a configuration file, named \"subscriptions.json\".\n"
+	printf "Please create this file first.\n"
+	printf "See the readme for instructions on how to create it.\n"
 	exit 1
 }
 
 [[ "$1" == "-h" || "$1" == "--help" ]] && help
+[ ! -f subscriptions.json ] && nojson
 
 saveifs=$IFS
 IFS=$'\n'