docs: add short how-to for running Moby on GCP

Signed-off-by: Rolf Neugebauer <rolf.neugebauer@docker.com>

docs/gcp.md

@@ -0,0 +1,59 @@
+# Using Moby on Google Cloud Platform (GCP)
+
+This is a quick guide to run Moby on GCP.
+
+## Setup
+
+You need the [Google Cloud SDK](https://cloud.google.com/sdk/)
+installed.  Either install it from the URL or view `brew` (on a Mac):
+```shell
+brew install google-cloud-sdk
+```
+
+Then, set up some environment variables (adjust as needed) and login:
+```shell
+export CLOUDSDK_CORE_PROJECT=<GCP project>
+export CLOUDSDK_COMPUTE_ZONE=europe-west1-d
+gcloud auth login
+```
+
+The authentication will redirect to a browser with Google login.
+
+## Build a moby image
+
+In the `alpine` subdirectory:
+```shell
+make gce
+```
+or (for a 4.4 kernel):
+```shell
+make LTS4.4=1 gce
+```
+You'll end up with `gce.img.tar.gz`. It's best to rename it to include the kernel version and the short commit tag or similar before uploading to GCP.
+
+If you don't need/want to compile Moby from source, you can do a `make get` in the top-level directory before `make gce`. This downloads most of the build artefacts like the kernel and initrd based on your git hash.
+
+## Upload an image and create a compute image
+
+The next step is to upload the image and create a Compute image from it.
+
+```shell
+TARBALL=gce.img-4.9-cb44fd1.tar.gz
+gsutil cp -a public-read ${TARBALL} gs://${NAME}/${TARBALL}
+# Note, GCP does not like "." in images names
+gcloud compute images create --source-uri \
+  https://storage.googleapis.com/rolf/${TARBALL} moby-4-9-cb44fd1
+```
+
+## Create an instance and connect to it
+
+With the image create, we can now create an instance and connect to
+the serial port.
+
+```shell
+gcloud compute instances create my-node-4-9 \
+  --image="moby-4-9-cb44fd1" --metadata serial-port-enable=true \
+  --machine-type="g1-small" --boot-disk-size=200
+
+gcloud compute connect-to-serial-port my-node-4-9
+```