feat(ci): add publish workflow (#22)

since Docker doesn't do builds anymore

.github/workflows/publish.yml

@@ -0,0 +1,35 @@
+name: Publish Docker image
+
+on:
+  release:
+    types: [published]
+
+jobs:
+  push_to_registry:
+    name: Push Docker image to Docker Hub
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check out the repo
+        uses: actions/checkout@v2
+
+      - name: Extract metadata (tags, labels) for Docker
+        id: meta
+        # https://github.com/docker/metadata-action
+        uses: docker/metadata-action@v3
+        with:
+          images: crccheck/hello-world
+
+      - name: Log in to DockerHub
+        uses: docker/login-action@v1
+        with:
+          username: ${{ secrets.DOCKER_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+
+      - name: Build and push
+        # https://github.com/docker/build-push-action
+        uses: docker/build-push-action@v2
+        with:
+          context: .
+          push: true
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}

README.md

@@ -1,5 +1,4 @@
-Hello World
-===========
+# Hello World
 
 This is a simple Docker image that just gives http responses on port 8000. It's
 small enough to fit on one floppy disk:
@@ -18,9 +17,7 @@ fresh environment in under a second. I like faster feedback loops.
 **THANK YOU** to the surprisingly large number of contributors that have made
 this better for everyone over the years.
 
-
-Sample Usage
-------------
+## Sample Usage
 
 ### Starting a web server on port 80