Add a CI for the docs, using the old version described in the docs th…

…emselves.

.github/workflows/build-docs.yml

@@ -0,0 +1,21 @@
+name: Build Docs
+on:
+  workflow_dispatch: {}
+jobs:
+  main:
+    name: Build & Deploy Docs
+    runs-on: ubuntu-20.04
+    permissions:
+      contents: write
+    steps:
+      - uses: actions/checkout@v3
+      - uses: w3c/spec-prod@v2
+        with:
+          TOOLCHAIN: bikeshed
+
+          # Modify as appropriate
+          GH_PAGES_BRANCH: main
+
+          # if your doc isn't in the root folder,
+          # or Bikeshed otherwise can't find it:
+          SOURCE: docs/index.bs