fix(make): add protoc target to top Makefile

Closes #670

Makefile

@@ -52,6 +52,10 @@ test-unit:
 test-style:
 	@scripts/validate-go.sh
 
+.PHONY: protoc
+protoc:
+	$(MAKE) -C _proto/ all
+
 .PHONY: clean
 clean:
 	@rm -rf $(BINDIR)

docs/developers.md

@@ -46,8 +46,7 @@ Note that you need to be on protobuf 3.x (`protoc --version`) and use the latest
 We use gRPC as an API layer. See `pkg/proto/hapi` for the generated Go code,
 and `_proto` for the protocol buffer definitions.
 
-To regenerate the Go files from the protobuf source, `cd _proto &&
-make`.
+To regenerate the Go files from the protobuf source, `make protoc`.
 
 ## Docker Images