Add Typhoon to Kubernetes GCE installation docs

[dghubble]

Description

Add Typhoon to Kubernetes GCE installation docs. Typhoon provides minimal and free Kubernetes clusters via Terraform module. It supports bare-metal, GCE, and Digital Ocean.

Clusters currently default to flannel for networking, but Calico v2.5.1 is an option on bare-metal, GCE, and Digital Ocean (DO w caveats) and runs in production. The default will be switched to "calico" soon.

Reviewer

Should this change be made in the v2.5 folder or do those not get republished often?

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[caseydavenport]

@dghubble thanks! This LGTM. You can add to v2.5 if you like and it will be published once the PR is merged.

Over to @emanic for docs review.

[dghubble]

Added to both master and v2.5

[emanic]

Thanks @dghubble ! LGTM. 👍