[doc] Reference the R doc in sphinx document site.

.github/workflows/doc.yml

@@ -0,0 +1,62 @@
+name: XGBoost-docs
+
+on: [push, pull_request]
+
+permissions:
+  contents: read  # to fetch code (actions/checkout)
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
+  cancel-in-progress: true
+
+env:
+  BRANCH_NAME: >-
+    ${{ github.event.pull_request.number && 'PR-' }}${{ github.event.pull_request.number || github.ref_name }}
+
+
+jobs:
+  # build-r-docs:
+  #   name: Build docs for the R package
+  #   runs-on:
+  #     - runs-on=${{ github.run_id }}
+  #     - runner=linux-amd64-cpu
+  #     - tag=r-tests-build-docs
+  #   steps:
+  #     # Restart Docker daemon so that it recognizes the ephemeral disks
+  #     - run: sudo systemctl restart docker
+  #     - uses: actions/checkout@v4
+  #       with:
+  #         submodules: "true"
+  #     - name: Log into Docker registry (AWS ECR)
+  #       run: bash ops/pipeline/login-docker-registry.sh
+  #     - run: bash ops/pipeline/build-r-docs.sh
+  #     - name: Upload R doc
+  #       run: |
+  #         python3 ops/pipeline/manage-artifacts.py upload \
+  #           --s3-bucket xgboost-docs \
+  #           --prefix ${BRANCH_NAME}/${PR_COMMIT_SHA} --make-public \
+  #           r-docs-${{ env.BRANCH_NAME }}.tar.bz2
+
+  trigger-rtd-build:
+    # needs: build-r-docs
+    name: Trigger Read The Docs build.
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          submodules: 'true'
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.10"
+          architecture: 'x64'
+      - run: |
+          pip3 install requests
+      - name: Trigger RTD
+        env:
+          RTD_AUTH: ${{ secrets.RTD_AUTH_TOKEN }}
+          TEST_SEC: ${{ secrets.TEST_SECRET }}
+        run: |
+          echo "branch name: ${BRANCH_NAME}"
+          echo "token: ${#RTD_AUTH}"
+          echo "test: ${#TEST_SEC}"
+          python3 ops/pipeline/trigger-rtd.py