Mention PR arduino-libraries#67 in README

Author: alranel

README.md

@@ -1,6 +1,7 @@
 👋 This is an **unofficial** fork of the official ArduinoBLE library, that incorporates the following pull requests originally submitted to the upstream repository:
 
 * https://github.com/arduino-libraries/ArduinoBLE/pull/53
+* https://github.com/arduino-libraries/ArduinoBLE/pull/67
 <!-- pull requests -->
 
 You can consider this as an experimental version of the library, that you can use to test features contributed by the community that haven't been merged yet.