Add assign-reviewers workflow

Author: jmulcahey-twilio

.github/workflows/assign-reviewers.yml

@@ -0,0 +1,19 @@
+name: Assign Reviewers
+
+on:
+  pull_request_target:
+    types: [opened, ready_for_review, reopened, synchronize, labeled, unlabeled]
+
+jobs:
+  reviewers:
+    name: Assign Reviewers
+    runs-on: ubuntu-latest
+    continue-on-error: true
+    steps:
+      - uses: actions/checkout@v2
+      - uses: zattoo/reviewers@v2
+        with:
+          token: ${{secrets.GITHUB_TOKEN}}
+          ignore: |
+            .DS_Store
+          source: ".owners"