Create auto-build.yml

Will this work?

.github/workflows/auto-build.yml

@@ -0,0 +1,31 @@
+name: publishmultipledockerimages
+on:
+  push:
+    branches: [ docker-mods ]
+    paths:
+      - '**/Dockerfile'
+
+jobs:
+  job1:
+    runs-on: ubuntu-latest
+    steps:
+      - name: checkout
+        uses: actions/checkout@v2
+        with:
+          fetch-depth: 0
+      - name: get changed files
+        id: getfile
+        run: |
+          echo "::set-output name=files::$(git diff-tree --no-commit-id --name-only -r ${{ github.sha }}| xargs)"
+
+      - name: echo the changed files
+        run: |
+          for i in ${{ steps.getfile.outputs.files }}
+            do
+              directory="$( echo $i | cut -d'/' -f1 -s )"
+              if [ -z "$directory" ]; then
+                continue # Skip root dir
+              elif [ "$i" == *.md ]; then
+                continue # Skip markdown files
+              docker build . --file $i --tag theme.park:$directory
+            done