Add cname and setup auto doc publishing on release (#162)

this should enable gh page to keep the custom domain when pushing doc.
As a separate improvement, also activate the documentation publication on release event.

.github/workflows/manual_docs.yml → .github/workflows/publish_docs.yml

@@ -1,6 +1,8 @@
 name: Create and publish documentation
 on:
   workflow_dispatch:
+  release:
+    types: [published]
 jobs:
   documentation:
     runs-on: ubuntu-latest
@@ -27,4 +29,5 @@ jobs:
         uses: peaceiris/actions-gh-pages@v3
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
-          publish_dir: ./docs/.vuepress/dist
+          publish_dir: ./docs/.vuepress/dist
+          cname: decoder.theengs.io