Adds help messaging via flag lib

main.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"bufio"
+	"flag"
 	"fmt"
 	"os"
 	"os/signal"
@@ -179,15 +180,30 @@ func handleSignals(c <-chan os.Signal) {
 	}
 }
 
-func main() {
-	// watch for signals, send them to be handled
-	c := make(chan os.Signal, 1)
-	signal.Notify(c, syscall.SIGTSTP, syscall.SIGCONT, syscall.SIGINT)
-	go handleSignals(c)
+func printHelp() {
+	header := `tally - spreadsheets
 
-	args := os.Args
-	if len(args) > 1 {
-		path := ExpandedAbsFilepath(args[1])
+Syntax: tally [filepath]
+
+Examples: tally
+          tally -h
+          tally ./my-tally-spreadsheet.tss
+          tally ./my-cool-csv.csv
+          tally ./my-cool-tsv.tsv
+
+filepath should be a path to a file that already exists. To create a new file, simply run tally with no arguments and then save the file however you like.
+`
+  _, _ = fmt.Fprintf(os.Stdout, header)
+	flag.PrintDefaults()
+}
+
+func main() {
+	flag.Usage = printHelp
+	flag.Parse()
+	args := flag.Args()
+
+	if len(args) > 0 {
+		path := ExpandedAbsFilepath(args[0])
 		ext := strings.ToLower(filepath.Ext(path))
 		switch ext {
 		case ".tss":
@@ -204,5 +220,11 @@ func main() {
 	} else {
 		wb = makeWorkbook("blank.tss")
 	}
+
+	// watch for signals, send them to be handled
+	c := make(chan os.Signal, 1)
+	signal.Notify(c, syscall.SIGTSTP, syscall.SIGCONT, syscall.SIGINT)
+	go handleSignals(c)
+
 	wb.Run()
 }