Add DockerHub description upon deployment

When docker images have been successfully deployed and tested, update the
DockerHub description with the current version of the README.md from github.
This is similar to what DockerHub Autobuild does, if it were used.

.github/workflows/test.yml

@@ -67,8 +67,9 @@ jobs:
     env:
       # Export environment variables for all stages.
       DOCKER_CLI_EXPERIMENTAL: enabled # for 'docker buildx'
-      DOCKER_BASE: mvdan/shfmt
+      DOCKER_USER: mvdan
       DOCKER_PASSWORD: ${{secrets.DOCKER_PASSWORD}}
+      DOCKER_REPO: shfmt
       # We use all platforms for which FROM images in our Dockerfile are
       # available.
       DOCKER_PLATFORMS: >
@@ -95,6 +96,7 @@ jobs:
           # Pushes tag - deploy tag name.
           echo "::set-env name=TAG::${GITHUB_REF/refs\/tags\//}"
         fi
+        echo "::set-env name=DOCKER_BASE::${DOCKER_USER}/${DOCKER_REPO}"
     - name: Install Docker buildx
       run: |
         set -vx
@@ -126,8 +128,8 @@ jobs:
     - name: Build multi-architecture Docker images with buildx
       run: |
         set -vx
-        username=${DOCKER_BASE/\/*/}
-        echo "$DOCKER_PASSWORD" | docker login -u="$username" --password-stdin
+        echo "$DOCKER_PASSWORD" \
+        | docker login -u="$DOCKER_USER" --password-stdin
 
         function buildx() {
           docker buildx build \
@@ -164,3 +166,30 @@ jobs:
             docker run --rm -v "$PWD:/mnt" -w '/mnt' "$image" -d myscript
           done
         done
+    - name: Install Node.js
+      uses: actions/setup-node@v1
+      with:
+        node-version: 13.x
+    - name: Update DockerHub description
+      run: |
+        set -vx
+        npm install [email protected]
+        node -e '
+          const fs = require("fs");
+          let readme = fs.readFileSync("README.md", "utf8");
+          let dockerHubAPI = require("docker-hub-api");
+          dockerHubAPI.login(
+            process.env.DOCKER_USER,
+            process.env.DOCKER_PASSWORD)
+          .then(function () {
+            let url = "https://github.com/" + process.env.GITHUB_REPOSITORY;
+            for (let ext of ["-alpine", ""]) {
+              let repo = process.env.DOCKER_REPO + ext;
+              dockerHubAPI.setRepositoryDescription(
+                process.env.DOCKER_USER,
+                repo,
+                {short: "Official " + repo + " images from " + url,
+                 full: readme});
+            }
+          });
+        '