create docs action

.github/workflows/docs.yml

@@ -0,0 +1,19 @@
+name: docs
+on: push
+jobs:
+  main:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v1
+      - uses: actions/setup-node@v1
+        with: { node-version: 12 }
+      - run: yarn
+      - run: yarn doc
+      - run: git add docs
+      - run: git commit -m docs
+        env: { EMAIL: octocat@github.com }
+      - run: git remote set-url github "https://${NAME}:${GITHUB_TOKEN}@github.com/${GITHUB_REPOSITORY}.git"
+        env:
+          NAME: octocat
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+      - run: git push github "${GITHUB_REF}"