Silence usage message on runtime error

main.go

@@ -77,6 +77,10 @@ func init() {
 }
 
 func run(c *cobra.Command, args []string) error {
+	// if we got past argument passing, then returned errors are runtime
+	// things (like file not found) that shouldn't trigger a usage message.
+	c.SilenceUsage = true
+
 	display = NewDisplay(noColour)
 
 	if len(searchRegexp) == 0 && len(searchFixed) == 0 {