Add Rubygems release workflow.

.github/workflows/release.yml

@@ -0,0 +1,23 @@
+name: Publish
+
+on:
+  release:
+    types: [published]
+
+jobs:
+  build:
+    name: Publish to Rubygems
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Set up Ruby 2.7
+        uses: actions/setup-ruby@v1
+        with:
+          ruby-version: 2.7
+
+      - name: Publish to RubyGems
+        uses: dawidd6/action-publish-gem@v1
+        with:
+          api_key: ${{secrets.RUBYGEMS_AUTH_TOKEN}}