Update README.md

Author: ldu2

README.md

@@ -4,3 +4,6 @@
 ## Usage | [Demo](https://ldu2.github.io/PDFRedactor/)
 You can simply redact your pdf file online. Simply go to the [Demo](https://ldu2.github.io/PDFRedactor/) page,
 and you can cover up whatever you want on your pdf file and download it as the modified version!
+
+## Note
+**When you upload your file, you are not sending it anywhere. The browser is only using it as input to edit it. The files only stays in your machine.**