Add spell check with reviewdog (misspell)

.github/workflows/reviewdog.yml

@@ -0,0 +1,15 @@
+# .github/workflows/reviewdog.yml
+name: reviewdog
+on: [pull_request]
+jobs:
+  misspell:
+    name: runner / misspell
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check out code.
+        uses: actions/checkout@v1
+      - name: misspell
+        uses: reviewdog/action-misspell@v1
+        with:
+          github_token: ${{ secrets.github_token }}
+          locale: "UK"