replaced github actions with streamline publication

.github/workflows/auto-publish.yml

@@ -0,0 +1,29 @@
+name: Build, and publish spec to GitHub Pages and /TR/
+
+on:
+  pull_request: {}
+  push:
+    branches: [main]
+    paths:
+      - 'images/**'
+      - 'index.bs'
+
+jobs:
+  main:
+    name: Build, Validate and Deploy
+    runs-on: ubuntu-20.04
+    steps:
+      - uses: actions/checkout@v2
+      - uses: w3c/spec-prod@v2
+        with:
+          TOOLCHAIN: bikeshed
+          SOURCE: index.bs
+          DESTINATION: index.html
+          GH_PAGES_BRANCH: gh-pages
+          W3C_ECHIDNA_TOKEN: ${{ secrets.W3C_TR_TOKEN }}
+          W3C_WG_DECISION_URL: https://lists.w3.org/Archives/Public/public-immersive-web-wg/2021Sep/0004.html
+          W3C_BUILD_OVERRIDE: |
+            status: WD
+
+# not set 'warning' to BUILD_FAIL_ON (not to cause error by bikeshed warning?)
+