Update Firefox link

Author: chall3ng3r

README.md

@@ -1,5 +1,5 @@
 # QRCoder for Chrome
-Quickly get QR Code of currently open page. Google Chrome version.
+Quickly get QR Code of currently open page. Google Chrome version. Firefox version https://github.com/chall3ng3r/QRCoder-Firefox
 
 My original idea of quickly getting QR code from the currently open page was using JS code in bookmark, published on my blog at https://www.orison.biz/blogs/chall3ng3r/2018/05/qr-coder-version-2/