all: add hello world builder

This adds a hello world builder as per:
go/luci/newroot/getting_started/3_first_builder_recipes?var.crbug-id=1384218&var.project-id=golang&var.cloud-project-name=golang-ci-luci&var.vm-service-account=luci-vm&var.swarming-app-id=chromium-swarm#4-add-a-builder

Change-Id: I24229f5ee3081bd57818efc085c70c1669ff81df
Reviewed-on: https://go-review.googlesource.com/c/build/+/456056
Reviewed-by: Carlos Amedee <carlos@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Auto-Submit: Carlos Amedee <carlos@golang.org>
TryBot-Bypass: Carlos Amedee <carlos@golang.org>
3 files changed
tree: 018adc78d7ae397a725caffab41a36542a2ad925
  1. generated/
  2. infra/
  3. recipes/
  4. .gitignore
  5. main.star
  6. README