Add example for excel to json with mapper from file and add docker support

examples/excel2json/Makefile

@@ -0,0 +1,11 @@
+DOCKER_IMAGE=cubetiq/node-excel2json
+
+build:
+	@echo "Building docker image..."
+	docker build . -t ${DOCKER_IMAGE}
+
+run:
+	@echo "Running container..."
+	docker run --rm -t ${DOCKER_IMAGE}
+
+.PHONY: build