Add instructions for building with docker #42

	name: Build CI

	env:
	downloadurl: https://s3.amazonaws.com/adafruit-circuit-python/gcc-arm-embedded_7-2018q2-1~xenial1_amd64.deb

	on:
	push:
	pull_request:
	release:
	types: [published]
	check_suite:
	types: [rerequested]

	jobs:
	test:
	runs-on: ubuntu-latest
	steps:
	- name: Dump GitHub context
	env:
	GITHUB_CONTEXT: ${{ toJson(github) }}
	run: echo "$GITHUB_CONTEXT"
	- uses: actions/cache@v1
	id: cache
	with:
	path: ../debs
	key: ${{ env.downloadurl }}-debs
	- name: Download gcc-arm-embedded
	if: steps.cache.outputs.cache-hit != 'true'
	run: \|
	mkdir ../debs
	wget -O ../debs/gcc-arm-embedded.deb $downloadurl
	- name: Install deps
	run: \|
	sudo dpkg -i ../debs/*.deb
	- name: Dump Versions
	run: \|
	gcc --version
	arm-none-eabi-gcc --version
	python3 --version
	lscpu
	- uses: actions/checkout@v1
	with:
	submodules: true
	- name: Build all
	run: \|
	make clean
	make all-boards -j $((1+`getconf _NPROCESSORS_ONLN`))
	- uses: actions/[email protected]
	with:
	name: seesaw-firmware
	path: fw

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