create first workflow action

.github/workflows/main.yml

@@ -0,0 +1,15 @@
+name: ci
+
+on: [push, pull_request]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+    
+    steps:
+    - uses: actions/checkout@v1
+    - name: test javascript packages
+      run: |
+        yarn install
+        yarn test