Build docs docker image when certain files change (#1306)

.github/workflows/docker.yml

@@ -0,0 +1,35 @@
+name: Build Docker image
+
+on:
+  workflow_dispatch:
+  push:
+    branches:
+      - current
+    paths:
+      - requirements.txt
+      - Dockerfile
+      - .github/workflows/docker.yml
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      -
+        name: Checkout source code
+        uses: actions/checkout@v2
+      -
+        name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v1
+      -
+        name: Login to DockerHub
+        uses: docker/login-action@v1
+        with:
+          username: ${{ secrets.DOCKER_USER }}
+          password: ${{ secrets.DOCKER_PASSWORD }}
+      -
+        name: Build and push
+        id: docker_build
+        uses: docker/build-push-action@v2
+        with:
+          push: true
+          tags: esphome/esphomedocs:latest