Update README to explain automatic package publishing from CircleCI

Author: floehopper

README.md

@@ -9,10 +9,12 @@
 
 * The default branch of the canonical repo is `develop`, but the default branch of this repo is `code-club-world`. This is to make it clear that the latter is where we should be making changes, to make it easier to bring in changes from the upstream repo, and so we can have our own CircleCI configuration to automatically build the app.
 
-* Commits pushed to the forked repo on GitHub trigger [builds on CircleCI](https://app.circleci.com/pipelines/github/RaspberryPiFoundation/scratch-gui) and a successful build results in the build output being deployed to GitHub Pages for this repo. The deployment makes use of an SSH key with write access to this repo.
+* Commits pushed to the forked repo on GitHub trigger [builds on CircleCI](https://app.circleci.com/pipelines/github/RaspberryPiFoundation/scratch-gui) and a successful build results in the build output being deployed to GitHub Pages for this repo and a version of the package being published to [the npm registry](https://www.npmjs.com/). The deployment makes use of an SSH key with write access to this repo.
 
 * The deployment adds the build output to the `gh-pages` branch in a sub-directory with the same name as the current branch. Thus the app is available at a URL including that sub-directory, e.g. https://raspberrypifoundation.github.io/scratch-gui/code-club-world/ for the default `code-club-world` branch.
 
+* The deployment publishes an organisation-scoped version of the package: [`@raspberrypifoundation/scratch-gui`](https://www.npmjs.com/package/@raspberrypifoundation/scratch-gui).  The publishing of the package makes use of an access token set as an environment variable (`NPM_TOKEN`) in the CircleCI project settings. The git repo is also tagged with the release version.
+
 ## Installation
 This requires you to have Git and Node.js installed.