cmd/config: Add examples and tutorials for config functions

- Add examples under `functions`
- Add built-in tutorial for functions

functions/examples/injection-tshirt-sizes/Makefile

@@ -0,0 +1,42 @@
+# Copyright 2019 The Kubernetes Authors.
+# SPDX-License-Identifier: Apache-2.0
+
+.PHONY: generate license fix vet fmt test build tidy image
+
+GOBIN := $(shell go env GOPATH)/bin
+
+build:
+	(cd image && go build -v -o $(GOBIN)/config-function .)
+
+all: generate license build fix vet fmt test lint tidy
+
+fix:
+	(cd image && go fix ./...)
+
+fmt:
+	(cd image && go fmt ./...)
+
+generate:
+	(which $(GOBIN)/mdtogo || go get sigs.k8s.io/kustomize/cmd/mdtogo)
+	(cd image && GOBIN=$(GOBIN) go generate ./...)
+
+license:
+	(which $(GOPATH)/bin/addlicense || go get github.com/google/addlicense)
+	$(GOPATH)/bin/addlicense  -y 2019 -c "The Kubernetes Authors." -f LICENSE_TEMPLATE .
+
+tidy:
+	(cd image && go mod tidy)
+
+lint:
+	(which $(GOBIN)/golangci-lint || go get github.com/golangci/golangci-lint/cmd/golangci-lint@v1.19.1)
+	(cd image && $(GOBIN)/golangci-lint run ./...)
+
+test:
+	(cd image && go test -cover ./...)
+
+vet:
+	(cd image && go vet ./...)
+
+image:
+	docker build image -t gcr.io/kustomize-functions/example-tshirt:v0.1.0
+	docker push gcr.io/kustomize-functions/example-tshirt:v0.1.0