Add Jest for JavaScript testing

frontend/README.md

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+# gochan.js development
+
+## Building
+You can technically use the npm build script directly for building gochan.js, but it's more convenient to just run `./build.py js` from the gochan repo root directory.
+
+If you want to build it without minification, run `./build.py js --nominify`. If you want to have it watch the JS files for changes and rebuild them when you make any in realtime, use the `--watch` flag.
+
+To install your gochan.js after building it, run `./build.py install --js`.
+
+## Testing
+Gochan unit testing with [Jest](https://jestjs.io) is still in its early stages and can be run by calling `npm run test` from the frontend directory.
+
+Depending on your npm version, you may need to run this if you get an error saying something like "Missing required argument #1" when you run `npm install` if you have the most up to date npm version available in your distro's repo.
+```
+sudo npm install -g n
+sudo n latest
+sudo npm install -g npm
+npm install
+```