Merge pull request #138 from dholbach/check-links

add Github Action to check links

.github/workflows/check-links.yaml

+name: "Check links"
+on: [pull_request, push]
+
+jobs:
+  docs:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v1
+    - name: Link Checker
+      id: lc
+      uses: peter-evans/link-checker@v1
+      with:
+        args: -r *.md *.yaml */*/*.go -x .cluster.local
+    - name: Fail if there were link errors
+      run: exit ${{ steps.lc.outputs.exit_code }}
+