docs: Update README with info about building local container image

CHANGELOG.md

@@ -8,6 +8,7 @@ Changelog
 - Improved error output when private key cannot be loaded
 - Updated example ZIP and CRX binaries because tests failed on differences in compression ratio (of exactly the same sources!)
 - Dropped use of runners on AppVeyor (Windows) and Cirrus CI (Linux & MacOS)
+- Added puppeteer.containerfile and usage info
 
 **v1.1.3** - 2020-11-06
 

README.md

@@ -147,7 +147,7 @@ Tests include optional support for checking if CRX files built by the module wil
 
 - make sure that Chrome or Chromium browser is already installed,
 - make sure that `CHROME_BIN` environment variable is set with path to the browser's executable,
-- make sure that `CHROME_POLICIES` environment variable points to exisitng directory tree used by the browser to read policies,
+- make sure that `CHROME_POLICIES` environment variable points to existing directory tree used by the browser to read policies,
 - optionally set `DEBUG` environment variable to `true`, to get additional output from test server,
 - optionally set `FILE_CHECK_DELAY` environment variable to number of milliseconds to wait for between various checks (defaults to 1500),
 - run `npm run puppeteer` to install additional dependencies.
@@ -156,14 +156,38 @@ Tests include optional support for checking if CRX files built by the module wil
 
 **WARNING:** Since there is no way to imitate installation process of a CRX file through the puppeteer (or is there?), test will try to create an `${CHROME_POLICIES}/managed/crx3-example-extension-test.json` policy file to "force install" it. That is why it is best to run whole thing in a virtual machine, e.g., using [`qemu`](https://www.qemu.org/), or in a container, e.g., using [`podman`](https://podman.io/) or [`docker`](https://www.docker.com/).
 
-Using `podman`:
+There is an official puppeteer docker image, but it's ~2 GB, which is unnecessarily huge. Using `podman` or `docker`, you can build image that's less than half of that size and is more than enough for testing if generated CRX3 works in a Chromium browser.
+
+### Testing with rootless `podman`
+
+First step is to prepare container image. This step is needed only once.
+
+```sh
+# 1. Prepare container, this step is needed only once
+podman build -t puppeteer -f puppeteer.containerfile
+# 2. Install puppeteer-core, this step is needed only once
+podman run --rm --init -v $(pwd):/app -w /app --userns=keep-id -it puppeteer:latest npm run puppeteer
+```
+
+After container image is ready, every time you want to run test, just use:
 
 ```sh
-podman run --rm -v $(pwd):/app -v $(pwd)/node_modules:/app/node_modules --userns=keep-id -it ahwayakchih/nodeapp:puppeteer xvfb-run npm test
+podman run --rm --init -v $(pwd):/app -w /app --userns=keep-id -it puppeteer:latest xvfb-run npm test
 ```
 
-Using `docker`:
+### Testing with `docker`
+
+First step is to prepare container image. This step is needed only once.
 
 ```sh
-docker run --rm -v $(pwd):/app -v $(pwd)/node_modules:/app/node_modules -it ahwayakchih/nodeapp:puppeteer xvfb-run npm test
+# 1. Prepare container, this step is needed only once
+docker build -t puppeteer -f puppeteer.containerfile
+# 2. Install puppeteer-core, this step is needed only once
+docker run --rm --init -v $(pwd):/app -w /app -it puppeteer:latest npm run puppeteer
 ```
+
+After container image is ready, every time you want to run test, just use:
+
+```sh
+docker run --rm --init -v $(pwd):/app -w /app -it puppeteer:latest xvfb-run npm test
+```