Add workflow for weekly linkcheck

Change-Id: I6b45566688b7d975347fa6a278d70c007fa35780
diff --git a/.github/workflows/linkcheck.yml b/.github/workflows/linkcheck.yml
new file mode 100644
index 0000000..4d39d1a
--- /dev/null
+++ b/.github/workflows/linkcheck.yml
@@ -0,0 +1,27 @@
+name: Check links
+on:
+  schedule:
+    - cron: '0 12 * * 3'
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  check:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+      - name: Set up Python
+        uses: actions/setup-python@v4
+        with:
+          python-version: '3.10'
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install -r requirements.txt
+      - name: Check external links
+        run: make linkcheck
+        env:
+          SPHINXOPTS: --color