Add publish action

.github/workflows/publish.yaml

@@ -0,0 +1,20 @@
+name: Publish to NPM
+
+on:
+  release:
+    types: [created]
+
+jobs:
+  publish-npm:
+    needs: build
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-node@v1
+        with:
+          node-version: 12
+          registry-url: https://registry.npmjs.org/
+      - run: npm i
+      - run: npm publish
+        env:
+          NODE_AUTH_TOKEN: ${{secrets.npm_token}}