adding rubocop workflow

.github/workflows/rubocop.yml

@@ -0,0 +1,28 @@
+name: Rubocop
+on: [push, pull_request]
+jobs:
+  rubocop:
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest]
+        ruby: [2.7]
+    runs-on: ${{ matrix.os }}
+    steps:
+      - uses: actions/checkout@v2
+      - uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: ${{ matrix.ruby }}
+          bundler-cache: true
+      - name: Install Rubocop
+        run: gem install rubocop code-scanning-rubocop
+      - name: Rubocop run --no-doc
+        run: |
+          bash -c "
+            rubocop --require code_scanning --format CodeScanning::SarifFormatter -o rubocop.sarif
+            [[ $? -ne 2 ]]
+          "
+      - name: Upload Sarif output
+        uses: github/codeql-action/upload-sarif@v1
+        with:
+          sarif_file: rubocop.sarif