add -v version flag

cmd/thanks/main.go

@@ -2,11 +2,31 @@ package main
 
 import (
 	"context"
+	"flag"
+	"fmt"
 
 	"git.gentoo.party/sam/thanks/internal/jobs"
 )
 
+var (
+	Version   = "development"
+	BuildTime = "unknown"
+)
+
+var flagVersion = false
+
+func init() {
+	flag.BoolVar(&flagVersion, "v", false, "show program version")
+}
+
 func main() {
+	flag.Parse()
+	if flagVersion {
+		fmt.Printf("version: %s\n", Version)
+		fmt.Printf("build time: %s\n", BuildTime)
+		return
+	}
+
 	myJob := jobs.BackupJob{
 		Source:     "zroot/home/sam/thanks",
 		Target:     "zrust/backup/weller/thanks",