Protobuf files used for transporting data in TootTally's spectator mode
First off, you need to install protobuf-compiler. It's easy to do in Ubuntu/Debian machines as it's a simple sudo apt install protobuf-compiler. You may read more on Protobuf's website for more info on compiling it natively on your machine.
Once you have protoc installed, simply run compile.sh (or copy-paste the command inside it into your shell) and have it generate the files in the cs and py directories. cs will contain the library for C# and py will contain the library for Python.