doc: infra diagram

[mmcloughlin]

Make a nice diagram 😄

https://diagrams.mingrammer.com/

[mmcloughlin]

from diagrams import Cluster, Diagram
from diagrams.gcp.analytics import PubSub
from diagrams.gcp.compute import GCE, Functions
from diagrams.gcp.database import Firestore
from diagrams.gcp.storage import GCS
from diagrams.gcp.devtools import SourceRepositories

with Diagram("Continuous Benchmarking"):
    # Go repository commits watched by Cloud Function and stored in Firestore.
    commits = Firestore("commits")
    SourceRepositories("go") >> Functions("watch") >> commits

    # Cloud Function watches new commits and enqueues work to a pubsub topic.
    jobs = PubSub("jobs")
    commits >> Functions("enqueue") >> jobs

    # Workers service the pubsub topic.
    workers = [GCE("worker") for i in range(3)]
    jobs >> workers