Add make src to quickly generate protobuf code

Makefile

 ALL:
 	@echo "THIS IS ONLY FOR DEVELOPMENT. DON'T USE IT"
 
+src:
+	mkdir -p src/java &&\
+	mkdir -p src/python &&\
+	mkdir -p src/cpp &&\
+	mkdir -p src/js&&\
+	protoc -Iproto --java_out=src/java --python_out=src/python --cpp_out=src/cpp --js_out=src/js $$(find ./proto -type f -iname "*.proto")
+
+clean:
+	rm -rf src
+.PHONY: clean src
+
 formatting:
 	clang-format -i $$(find proto/ -type f -iname "*.proto")
 

README_SETUP.md

@@ -17,6 +17,11 @@ contains all necessary configuration.
 We use [buf](https://docs.buf.build/) for linting. Run `buf lint`. The
 `buf.yaml` contains all necessary configuration.
 
+## Source code generation
+
+`make src` generates the protobuf code for Java, C++, Python and JavaScript using
+the locally installed `protoc`.
+
 ## Docs
 
 We use [cmake](https://cmake.org) as build tool for the documenation and