task: add a workflow that validates docs for PRs (#1123)

.github/workflows/build_doc_prs.yaml

@@ -0,0 +1,17 @@
+name: PR -> Build Docs
+
+on:
+  pull_request:
+    paths:
+      - website/**
+
+jobs:
+  validate:
+
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - name: setup git config
+        run: |
+          # Build the site
+          cd website && yarn && yarn build