create gh release on tag

For #210

*   update changelog format so that `parse-changelog` is happy.
*   add the example from taiki-e/create-gh-release-action verbatim.
    Fingers crossed it works in my setup.

.github/workflows/release.yml

@@ -0,0 +1,19 @@
+name: Release
+
+on:
+  push:
+    tags:
+      - v[0-9]+.*
+
+jobs:
+  create-release:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: taiki-e/create-gh-release-action@v1
+        with:
+          # (Optional) Path to changelog.
+          changelog: CHANGELOG.md
+        env:
+          # (Required) GitHub token for creating GitHub Releases.
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}