Add prebuilt osx aarch64 version of protoc

Precondition: maven is installed (i.e. $ brew install maven)

Download the attached zip file and execute the following lines in the according directory:
$ unzip protoc-osx-aarch64-install.zip
$ cd protoc-osx-aarch64-install/
$ mvn install

Full Changelog: https://github.com/yecho/protobuf/commits/v3.5.1.1-protoc-osx-aarch64