Add sauce labs browser test matrix to readme

[skip ci]

Signed-off-by: Christoph Wurst <christoph@winzerhof-wurst.at>

README.md

@@ -3,6 +3,8 @@
 [![Build Status](https://travis-ci.org/nextcloud/twofactor_totp.svg?branch=master)](https://travis-ci.org/nextcloud/twofactor_totp)
 [![Scrutinizer Code Quality](https://scrutinizer-ci.com/g/nextcloud/twofactor_totp/badges/quality-score.png?b=master)](https://scrutinizer-ci.com/g/nextcloud/twofactor_totp/?branch=master)
 
+[![Sauce Test Status](https://saucelabs.com/browser-matrix/nextcloud-totp.svg)](https://saucelabs.com/u/nextcloud-totp)
+
 Tested with the following apps:
 * [FreeOTP Authenticator](https://freeotp.github.io/) (open source) Availabe via [F-droid](https://f-droid.org/repository/browse/?fdfilter=otp&fdid=org.fedorahosted.freeotp), [Google Play](https://play.google.com/store/apps/details?id=org.fedorahosted.freeotp), and [Apple's App Store](https://itunes.apple.com/us/app/freeotp-authenticator/id872559395?mt=8)
 * [OTP Authenticator](https://github.com/0xbb/otp-authenticator) (open source) Availabe via [F-Droid](https://f-droid.org/repository/browse/?fdfilter=totp&fdid=net.bierbaumer.otp_authenticator) and [Google Play](https://play.google.com/store/apps/details?id=net.bierbaumer.otp_authenticator). It features a built-in QR-code reader.