add docker build files

.dockerignore

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+node_modules/

.github/workflows/docker.yml

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+name: Docker build
+
+on:
+  push:
+    branches: [ main ]
+
+jobs:
+  image:
+    name: Build Docker image
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v2
+
+      - name: Log into registry ${{ env.REGISTRY }}
+        uses: docker/login-action@v1
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Build and push Docker image
+        uses: docker/build-push-action@v2
+        with:
+          context: .
+          push: ${{ github.event_name != 'pull_request' }}
+          tags: |
+            ghcr.io/apparyllisorg/spot:${{ github.sha }}
+            ghcr.io/apparyllisorg/spot:latest
+          labels: ${{ steps.meta.outputs.labels }}

Dockerfile

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+FROM alpine:latest
+
+RUN apk add nodejs-current yarn
+
+WORKDIR /app
+COPY package.json yarn.lock /app/
+RUN yarn
+
+COPY . /app
+
+CMD ["node", "bot.js"]