Add instructions for configuring GCR (#182)

We should eventually add instructions for other registries, but this
will help people using GCR to get started.

creating-a-kubernetes-cluster.md

@@ -62,28 +62,6 @@ To use a k8s cluster running in GKE:
         --user=$GCP_USER
     ```
 
-7. Enable the GCR API:
-
-   ```shell
-   gcloud --project=$PROJECT_ID service-management enable containerregistry.googleapis.com
-   ```
-
-8. Install the `docker-credential-gcr` helper so Docker (and Bazel) can
-   authenticate with GCR:
-
-   ```shell
-   gcloud components install docker-credential-gcr
-   ```
-
-9. Add the GCR credentials to the Docker config file:
-
-   ```shell
-   docker-credential-gcr configure-docker
-   ```
-
-Now you can use `gcr.io/$PROJECT_ID` as your Docker repo and your GKE
-cluster will automatically pull from it.
-
 ## Minikube
 
 1. [Install and configure
@@ -106,10 +84,10 @@ minikube start \
 
 You can use Google Container Registry as the registry for a Minikube cluster.
 
-1. [Set up a GCR repo](TODO). Export the environment variable  `PROJECT_ID`
-   as the name of your project. Also export `GCR_DOMAIN` as the domain name
-   of your GCR repo. This will be either `gcr.io` or a region-specific variant
-   like `us.gcr.io`.
+1. [Set up a GCR repo](setting-up-a-docker-registry.md). Export the environment
+   variable  `PROJECT_ID` as the name of your project. Also export `GCR_DOMAIN`
+   as the domain name of your GCR repo. This will be either `gcr.io` or a
+   region-specific variant like `us.gcr.io`.
 
    ```shell
    export PROJECT_ID=elafros-demo-project

setting-up-a-docker-registry.md

@@ -0,0 +1,80 @@
+# Setting Up A Docker Registry
+
+This document explains how to use different Docker registries with Elafros. It
+assumes you have gone through the steps listed in
+[DEVELOPMENT.md](/DEVELOPMENT.md) to set up your development environment (or
+that you at least have installed `go`, set `GOPATH`, and put `$GOPATH/bin` on
+your `PATH`).
+
+It currently only contains instructions for [Google Container Registry
+(GCR)](https://cloud.google.com/container-registry/), but you should be able to
+use any Docker registry.
+
+## Google Container Registry (GCR)
+
+### Required Tools
+
+Install the following tools:
+
+1.  [`gcloud`](https://cloud.google.com/sdk/downloads)
+1.  [`docker-credential-gcr`](https://github.com/GoogleCloudPlatform/docker-credential-gcr)
+
+    If you installed `gcloud` using the archive or installer, you can install
+    `docker-credential-gcr` like this:
+
+    ```shell
+    gcloud components install docker-credential-gcr
+    ```
+
+    If you installed `gcloud` using a package manager, you may need to install
+    it with `go get`:
+
+    ```shell
+    go get github.com/GoogleCloudPlatform/docker-credential-gcr
+    ```
+
+    If you used `go get` to install and `$GOPATH/bin` isn't already in `PATH`,
+    add it:
+
+    ```shell
+    export PATH=$PATH:$GOPATH/bin
+    ```
+
+### Setup
+
+1.  If you haven't already set up a GCP project, create one and export its name
+    for use in later commands.
+
+    ```shell
+    export PROJECT_ID=my-project-name
+    gcloud projects create "${PROJECT_ID}"
+    ```
+
+1.  Enable the GCR API.
+
+    ```shell
+    gcloud --project="${PROJECT_ID}" service-management enable \
+    containerregistry.googleapis.com
+    ```
+
+1.  Hook up your GCR credentials. Note that this may complain if you don't have
+    the docker CLI installed, but it is not necessary and should still work.
+
+    ```shell
+    docker-credential-gcr configure-docker
+    ```
+
+1.  If you need to, update your `DOCKER_REPO_OVERRIDE` in your `.bashrc`. It
+    should now be
+
+    ```shell
+    export DOCKER_REPO_OVERRIDE='us.gcr.io/<your-project-id>'
+    ```
+
+    (You may need to use a different region than `us` if you didn`t pick a`us`
+    Google Cloud region.)
+
+1.  You may need to run `bazel clean` after updating your `DOCKER_REPO_OVERRIDE`
+    environment variable for `bazel` to pick up the change.
+
+That's it, you're done!