Only run docker build workflow on master branch

.github/workflows/docker.yml

@@ -0,0 +1,35 @@
+name: docker
+
+on:
+  push:
+    branches:
+      - master
+
+env:
+  GO_VERSION: 1.18
+  CGO_ENABLED: 0
+  IMAGE_REPOSITORY: sosedoff/pgweb
+
+jobs:
+  docker-build:
+    name: docker images
+    runs-on: ubuntu-latest
+    timeout-minutes: 30
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v3
+
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v2
+
+      - name: Configure docker build context
+        uses: docker/setup-buildx-action@v2
+
+      - name: Build docker images
+        uses: docker/build-push-action@v2
+        with:
+          context: .
+          push: false
+          tags: pgweb:latest
+          platforms: linux/amd64,linux/arm64,linux/arm/v5,linux/arm/v7