builder/googlecompute: Add website docs

website/source/docs/builders/googlecompute.markdown

+---
+layout: "docs"
+---
+
+# Google Compute Builder
+
+Type: `googlecompute`
+
+The `googlecompute` builder is able to create new [images](https://developers.google.com/compute/docs/images)
+for use with [Google Compute Engine](https://cloud.google.com/products/compute-engine).
+
+## Basic Example
+
+Below is a fully functioning example. It doesn't do anything useful, since no provisioners are defined, but it will effectively repackage an GCE image.
+
+<pre class="prettyprint">
+{
+  "type": "googlecompute",
+  "bucket_name": "packer-images",
+  "client_secrets_file": "client_secret_XXXXXX-XXXXXX.apps.googleusercontent.com.json",
+  "private_key_file": "XXXXXX-privatekey.pem",
+  "project_id": "my-project",
+  "source_image": "debian-7-wheezy-v20131014",
+  "zone": "us-central1-a"
+}
+</pre>
+
+## Configuration Reference
+
+Configuration options are organized below into two categories: required and optional. Within
+each category, the available options are alphabetized and described.
+
+Required:
+
+* `bucket_name` (string) - The Google Cloud Storage bucket to store images.
+* `client_secrets_file` (string) - The client secrets file.
+* `private_key_file` (string) - The service account private key.
+* `project_id` (string) - The GCE project id.
+* `source_image` (string) - The source image. Example `debian-7-wheezy-v20131014`.
+* `zone` (string) - The GCE zone.
+
+Optional:
+
+* `image_name` (string) - The unique name of the resulting image. Defaults to `packer-{{timestamp}}`.
+* `image_description` (string) - The description of the resulting image.
+* `machine_type` (string) - The machine type. Defaults to `n1-standard-1`.
+* `network` (string) - The Google Compute network. Defaults to `default`.
+* `passphrase` (string) - The passphrase to use if the `private_key_file` is encrypted.
+* `ssh_port` (int) - The SSH port. Defaults to `22`.
+* `ssh_timeout` (string) - The time to wait for SSH to become available. Defaults to `1m`.
+* `ssh_username` (string) - The SSH username. Defaults to `root`.
+* `state_timeout` (string) - The time to wait for instance state changes. Defaults to `5m`.
+
+## Gotchas
+
+Centos images have root ssh access disabled by default. Set `ssh_username` to any user, which will be created by packer with sudo access.
+
+The machine type must have a scratch disk, which means you can't use an `f1-micro` or `g1-small` to build images.