Fix idevicebackup2 man page

Thanks to @SCOTT-HAMILTON for pointing this out.
diff --git a/docs/idevicebackup2.1 b/docs/idevicebackup2.1
index abbe38a..79b6dc4 100644
--- a/docs/idevicebackup2.1
+++ b/docs/idevicebackup2.1
@@ -47,7 +47,7 @@
 restore system files, too.
 .TP
 .B \t\-\-no\-reboot
-reboot the system when done.
+do NO reboot the system when done.
 .TP
 .B \t\-\-copy
 create a copy of backup folder before restoring.