Add github actions for ci

[ryanio]

hey :) I found your gh actions workflow that you mentioned.

I found two things:

1. actions/checkout was before actions/setup-node
2. bootstrap was misspelled

I also added your browser tests and made sure the workflow runs on updates to PRs and new tags.

[ricmoo]

Thanks! :)

I think another problem is I hadn't allowed third-party, which may be required for the checkout/setup actions?

I've added some of your changes for the next push. I'm trying to get the basics working before I enable the browser, because they chew up a lot of CPU time. :)

[ryanio]

np! did you see the checks? https://github.com/ethers-io/ethers.js/pull/853/checks?check_run_id=717835576

[ricmoo]

Yeah, just saw them. That's awesome. So, I will prolly pull your changes in now... I originally just copied the order their UI build for me.

Few quick questions:

• Does the filename matter? build.yml vs. nodejs.yml? Or is that just something you already had in another project? Or the recommended standard?
• What is the easiest way to see how many CI credits I have left?

[ryanio]

Filename doesn't matter but you can customize the name of the workflow and the name of the jobs for how you'd like them to display in the check. also shows in the sidebar here https://github.com/ethers-io/ethers.js/actions

yeah I used my best defaults. also the img src of the readme badge changes with the name: of the workflow. you can use the "Create status badge" btn on the check to generate:

Free for public repos is pretty amazing 🥇 💯 🔥

[ryanio]

It's also trivial to run cron jobs so we have a nightly test run with fresh deps in ethereumjs-vm that's pretty cool (VM Nightly).

[ricmoo]

So... much... faster. :)

[ryanio]

nice great it's passing! ✅

[ryanio]

yeah i have no idea how they got it so fast but it's probably the best part