ci: setup automatic publishing

.github/workflows/release.yml

@@ -0,0 +1,30 @@
+name: Release
+
+on:
+  push:
+    tags:
+      - v*
+
+permissions:
+  contents: read # to fetch code (actions/checkout)
+
+jobs:
+  push:
+    permissions:
+      contents: write
+      id-token: write
+    if: github.repository == 'ackama/lighthouse-matchers'
+    runs-on: ubuntu-latest
+    steps:
+      - name: Harden Runner
+        uses: step-security/harden-runner@v2
+        with:
+          egress-policy: audit
+      - uses: actions/checkout@v4
+        with:
+          persist-credentials: false
+      - uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: '3.2'
+          bundler-cache: true
+      - uses: rubygems/release-gem@v1

README.md

@@ -121,6 +121,12 @@ for detailed instructions.
 
 This gem endeavours to follow Semantic Versioning 2.0 as defined at https://semver.org/.
 
+## Releasing
+
+Releases are done automatically by GitHub Actions when a new tag is pushed to the repository.
+
+To release a new version, create a pull request updating the "Unreleased" section of `CHANGELOG.md` file to reflect the upcoming version and expected release date, and to update the version number in `lib/lighthouse/matchers/version.rb`. Once the pull request is merged, create a new tag in the format `vX.Y.Z`, which will trigger GitHub Actions to publish the new version to RubyGems.
+
 ## License
 
 lighthouse-matchers is copyright © 2019 Ackama Group Ltd.