Update Contributing docs for recent go changes (#58)

As we migrate to go modules and update linter configs, I add a new page to give contributor more guidance on basic setup and development flow.

Signed-off-by: Jiaxin Shan <seedjeffwan@gmail.com>

CONTRIBUTING.md

@@ -0,0 +1,61 @@
+## Contributing
+
+mxnet-operator uses go modules and supports both v1beta1 and v1. We suggest to use golang 1.13.x for development. 
+Make sure you enable `GO111MODULE`.
+
+### Setup development environment
+
+```shell
+mkdir -p ${GOPATH}/src/github.com/kubeflow
+cd ${GOPATH}/src/github.com/kubeflow
+git clone https://github.com/${GITHUB_USER}/mxnet-operator.git
+```
+
+### Download go mods
+
+Some utility modules like `code-generator` will be used in hack scripts, 
+it's better to download all dependencies for the first time.
+
+```shell
+go mod download
+```
+
+### Build the operator locally
+
+```shell
+go build -o mxnet-operator.v1beta1 github.com/kubeflow/mxnet-operator/cmd/mxnet-operator.v1beta1
+go build -o mxnet-operator.v1 github.com/kubeflow/mxnet-operator/cmd/mxnet-operator.v1
+```
+
+### Build container image
+
+```shell
+# It requires you to build binary locally first.
+docker build -t ${your_dockerhub_username}/mxnet-operator:v1 .
+```
+
+### Test Binaries locally
+
+```shell
+./mxnet-operator.v1beta1 --kubeconfig=$HOME/.kube/config
+```
+
+### Before code check-in
+
+There're several steps to follow before you submit PR.
+
+```shell
+# Verify codegen in case you change api but for get to generate new packages.
+./hack/verify-codegen.sh
+
+# Lint codes
+golangci-lint run --config=linter_config.yaml ./...
+```
+
+### Regenerate clients and apis
+
+If you make changes under `/pkg/apis`, you probably need to regenerate clients and apis.
+
+```shell
+./hack/update-codegen.sh
+```

README.md

@@ -278,7 +278,7 @@ server-76no-1
 
 ## Contributing
 
-Please refer to the [developer_guide](https://github.com/kubeflow/tf-operator/blob/master/developer_guide.md)
+Please refer to the [Contributing Document](./CONTRIBUTING.md)
 
 ## Community
 

hack/update-codegen.sh

@@ -80,4 +80,6 @@ echo "Generating defaulters for v1"
   --output-package github.com/kubeflow/mxnet-operator/pkg/apis/mxnet/v1
 
 # Copy everything back.
-cp -a "${TEMP_DIR}/${ROOT_PKG}/." "${SCRIPT_ROOT}/"
+cp -a "${TEMP_DIR}/${ROOT_PKG}/." "${SCRIPT_ROOT}/"
+# Clean up binaries we build for update codegen
+rm ./defaulter-gen