cmd/getgo: display that -i stands for interactive mode

Change-Id: Ia6d8b0e9b2a355d2c4b41634fd51de51187be833
Reviewed-on: https://go-review.googlesource.com/51931
Reviewed-by: Kevin Burke <kev@inburke.com>
diff --git a/cmd/getgo/main.go b/cmd/getgo/main.go
index d14f329..58cfbdf 100644
--- a/cmd/getgo/main.go
+++ b/cmd/getgo/main.go
@@ -17,7 +17,7 @@
 )
 
 var (
-	interactive = flag.Bool("i", false, "Prompt for inputs.")
+	interactive = flag.Bool("i", false, "Interactive mode, prompt for inputs.")
 	verbose     = flag.Bool("v", false, "Verbose.")
 	setupOnly   = flag.Bool("skip-dl", false, "Don't download - only set up environment variables")
 	goVersion   = flag.String("version", "", `Version of Go to install (e.g. "1.8.3"). If empty, uses the latest version.`)