Enhance documentation

Signed-off-by: CrazyMax <crazy-max@users.noreply.github.com>

docs/advanced/export-docker.md

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+# Export image to Docker
+
+You may want your build result to be available in the Docker client through `docker images` to be able to use it
+in another step of your workflow:
+
+```yaml
+name: ci
+
+on:
+  push:
+    branches:
+      - 'master'
+
+jobs:
+  docker:
+    runs-on: ubuntu-latest
+    steps:
+      -
+        name: Checkout
+        uses: actions/checkout@v2
+      -
+        name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v1
+      -
+        name: Build
+        uses: docker/build-push-action@v2
+        with:
+          context: .
+          load: true
+          tags: myimage:latest
+      -
+        name: Inspect
+        run: |
+          docker image inspect myimage:latest
+```