ci(github-actions): add ci to build and push docker image

.github/workflows/docker.yml

@@ -0,0 +1,58 @@
+name: docker
+
+on:
+  schedule:
+    - cron: '0 3 5 * *' # every friday at 3am
+  push:
+    branches:
+      - '**'
+    tags:
+      - '*.*.*'
+  pull_request:
+    branches:
+      - 'master'
+
+jobs:
+  docker:
+    runs-on: ubuntu-latest
+    steps:
+      -
+        name: Checkout
+        uses: actions/checkout@v2
+      -
+        name: Set up dynamic build ARGs
+        id: getargs
+        run: echo "::set-output name=version::$(cat ./stable/VERSION)"
+      -
+        name: Docker meta
+        id: meta
+        uses: docker/metadata-action@v3
+        with:
+          # list of Docker images to use as base name for tags
+          images: |
+            m0wer/tiddlywiki
+          # generate Docker tags based on the following events/attributes
+          tags: |
+            type=raw,value=latest
+            type=schedule
+            type=ref,event=branch
+            type=ref,event=pr
+            type=semver,pattern={{version}}
+            type=semver,pattern={{major}}.{{minor}}
+            type=semver,pattern={{major}}
+            type=sha
+      -
+        name: Login to DockerHub
+        if: github.event_name != 'pull_request'
+        uses: docker/login-action@v1 
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+      -
+        name: Build and push
+        uses: docker/build-push-action@v2
+        with:
+          platforms: linux/amd64
+          push: ${{ github.event_name != 'pull_request' }}
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}