create check-readme-in-sync workflow

.github/workflows/check-readme-in-sync.yml

@@ -0,0 +1,34 @@
+# Reference: https://github.com/Yash-Singh1/eslint-plugin-userscripts/blob/main/.github/workflows/readme-in-sync.yml
+
+name: Check if README and docs/README are in sync
+
+on:
+  push:
+    branches:
+      - master
+      - develop
+  pull_request:
+    branches:
+      - master
+      - develop
+
+jobs:
+  check:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v2
+
+      - name: Check for difference in README.md and docs/README.md
+        run: |
+          if [ -z "$(diff README.md docs/README.md --brief)" ]
+          then
+            echo "README.md and docs/README.md are in sync"
+          else
+            echo "Make sure that README.md and docs/README.md are in sync"
+            echo
+            echo "Difference:"
+            echo
+            diff README.md docs/README.md -u
+            exit 1
+          fi