add Makefiles and document their use in the README

Signed-off-by: Gaetan de Villele <gdevillele@gmail.com>

.gitignore

@@ -1 +1,2 @@
 .DS_Store
+/build

Makefile

@@ -0,0 +1,19 @@
+#
+# github.com/docker/cli 
+#
+
+.PHONY: build clean cross
+
+# build the CLI
+build: clean
+	@go build -o ./build/docker ./cmd/docker
+
+# remove build artifacts
+clean:
+	@rm -rf ./build
+
+# build the CLI for multiple architectures
+cross: clean
+	@gox -output build/docker-{{.OS}}-{{.Arch}} \
+		 -osarch="linux/arm linux/amd64 darwin/amd64 windows/amd64" \
+		 ./cmd/docker

README.md

@@ -10,6 +10,57 @@ It's composed of 3 main folders
 * `/client` - the API client, used by `/cli`.
 * `/cmd/docker` - the entrypoint of the cli, aka the main.
 
+Development
+===========
+
+### Build locally
+
+```
+$ make build
+```
+
+```
+$ make clean
+```
+
+You will need [gox](https://github.com/mitchellh/gox) for this one:
+
+```
+$ make cross
+```
+
+If you don't have [gox](https://github.com/mitchellh/gox), you can use the "in-container" version of `make cross`, listed below.
+
+### Build inside container
+
+```
+$ make -f docker.Makefile build
+```
+
+```
+$ make -f docker.Makefile clean
+```
+
+```
+$ make -f docker.Makefile cross
+```
+
+### In-container development environment
+
+```
+$ make -f docker.Makefile dev
+```
+
+Then you can use the [build locally](#build-locally) commands:
+
+```
+$ make build
+```
+
+```
+$ make clean
+```
+
 Legal
 =====
 *Brought to you courtesy of our legal counsel. For more context,

docker.Makefile

@@ -0,0 +1,30 @@
+#
+# github.com/docker/cli
+#
+# Makefile for developing using Docker
+#
+
++.PHONY: build_docker_image build clean cross dev
+
+DEV_DOCKER_IMAGE_NAME = docker_cli_dev
+
+# build docker image (dockerfiles/Dockerfile.build)
+build_docker_image:
+	@docker build -t $(DEV_DOCKER_IMAGE_NAME) -f ./dockerfiles/Dockerfile.build . > /dev/null
+
+# build executable using a container
+build: build_docker_image
+	@echo "WARNING: this will drop a Linux executable on your host (not a macOS of Windows one)"
+	@docker run --rm -v `pwd`:/go/src/github.com/docker/cli $(DEV_DOCKER_IMAGE_NAME) make build
+
+# clean build artifacts using a container
+clean: build_docker_image
+	@docker run --rm -v `pwd`:/go/src/github.com/docker/cli $(DEV_DOCKER_IMAGE_NAME) make clean
+
+# build the CLI for multiple architectures using a container
+cross: build_docker_image
+	@docker run --rm -v `pwd`:/go/src/github.com/docker/cli $(DEV_DOCKER_IMAGE_NAME) make cross
+
+# start container in interactive mode for in-container development
+dev: build_docker_image
+	@docker run -ti -v `pwd`:/go/src/github.com/docker/cli $(DEV_DOCKER_IMAGE_NAME) ash

dockerfiles/Dockerfile.build

@@ -1,7 +1,7 @@
 
 FROM    golang:1.8-alpine
 
-RUN     apk add -U git
+RUN     apk add -U git make
 
 RUN     go get github.com/LK4D4/vndr && \
         cp /go/bin/vndr /usr/bin && \