Add workflow to draft release notes (#20)

Author: kentaro-m

.github/release-drafter.yml

@@ -0,0 +1,4 @@
+template: |
+  ## Changes
+
+  $CHANGES

.github/workflows/release-note.yml

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+name: Release Drafter
+
+on:
+  push:
+    branches:
+      - master
+
+jobs:
+  update_release_draft:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: release-drafter/release-drafter@v5
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}