write docs for cutWALUntil and wal2json binaries

scripts/cutWALUntil/main.go

@@ -1,3 +1,10 @@
+/*
+	cutWALUntil is a small utility for cutting a WAL until the given height
+	(inclusively). Note it does not include last cs.EndHeightMessage.
+
+	Usage:
+			cutWALUntil <path-to-wal> height-to-stop <output-wal>
+*/
 package main
 
 import (
@@ -10,27 +17,32 @@ import (
 )
 
 func main() {
+	if len(os.Args) < 4 {
+		fmt.Println("3 arguments required: <path-to-wal> height-to-stop <output-wal>")
+		os.Exit(1)
+	}
+
 	var heightToStop uint64
 	var err error
 	if heightToStop, err = strconv.ParseUint(os.Args[2], 10, 64); err != nil {
-		panic(fmt.Errorf("failed to parse height: %v (format: cutWALUntil in heightToStop out)", err))
+		panic(fmt.Errorf("failed to parse height: %v", err))
 	}
 
 	in, err := os.Open(os.Args[1])
 	if err != nil {
-		panic(fmt.Errorf("failed to open WAL file: %v (format: cutWALUntil in heightToStop out)", err))
+		panic(fmt.Errorf("failed to open input WAL file: %v", err))
 	}
 	defer in.Close()
 
 	out, err := os.Create(os.Args[3])
 	if err != nil {
-		panic(fmt.Errorf("failed to open WAL file: %v (format: cutWALUntil in heightToStop out)", err))
+		panic(fmt.Errorf("failed to open output WAL file: %v", err))
 	}
 	defer out.Close()
 
 	enc := cs.NewWALEncoder(out)
-
 	dec := cs.NewWALDecoder(in)
+
 	for {
 		msg, err := dec.Decode()
 		if err == io.EOF {

scripts/wal2json/main.go

@@ -1,3 +1,9 @@
+/*
+	wal2json converts binary WAL file to JSON.
+
+	Usage:
+			wal2json <path-to-wal>
+*/
 package main
 
 import (
@@ -10,6 +16,11 @@ import (
 )
 
 func main() {
+	if len(os.Args) < 2 {
+		fmt.Println("missing one argument: <path-to-wal>")
+		os.Exit(1)
+	}
+
 	f, err := os.Open(os.Args[1])
 	if err != nil {
 		panic(fmt.Errorf("failed to open WAL file: %v", err))