Added to Usage section in README.md. #46

	name: CI
	on: [push, pull_request]

	jobs:
	build-linux-gcc:
	runs-on: ubuntu-18.04
	steps:
	- uses: actions/checkout@v1
	- name: install dependencies
	run: \|
	sudo apt-get update
	sudo apt-get install -qq libsdl2-dev
	- name: build sowon
	run: \|
	make
	env:
	CC: gcc
	build-linux-clang:
	runs-on: ubuntu-18.04
	steps:
	- uses: actions/checkout@v1
	- name: install dependencies
	run: \|
	sudo apt-get update
	sudo apt-get install -qq libsdl2-dev
	- name: build sowon
	run: \|
	make
	env:
	CC: clang
	build-macos:
	runs-on: macOS-latest
	steps:
	- uses: actions/checkout@v1
	- name: install dependencies
	run: brew install sdl2 pkg-config
	- name: build sowon
	run: \|
	make
	env:
	CC: clang
	build-windows-msvc:
	runs-on: windows-2019
	steps:
	- uses: actions/checkout@v1
	# this runs vcvarsall for us, so we get the MSVC toolchain in PATH.
	- uses: seanmiddleditch/gha-setup-vsdevenv@master
	- name: download sdl2
	run: \|
	curl -fsSL -o SDL2-devel-2.0.12-VC.zip https://www.libsdl.org/release/SDL2-devel-2.0.12-VC.zip
	tar -xf SDL2-devel-2.0.12-VC.zip
	mv SDL2-2.0.12 SDL2
	- name: build sowon
	shell: cmd
	run: \|
	./build_msvc.bat
	# TODO: FreeBSD build is broken
	# build-freebsd:
	# runs-on: macos-latest
	# name: FreeBSD LLVM Clang build
	# steps:
	# - uses: actions/checkout@v2
	# - name: Build on FreeBSD
	# id: build
	# uses: vmactions/freebsd-vm@v0.0.9
	# with:
	# usesh: true
	# prepare: pkg install -y sdl2 pkgconf
	# run: \|
	# freebsd-version
	# make

Provide feedback