docs: add multi-platform build example to README

Signed-off-by: Vedant Madane <vedant.madane@gmail.com>

README.md

@@ -13,6 +13,7 @@ GitHub Action to install [QEMU](https://github.com/qemu/qemu) static binaries.
 ___
 
 * [Usage](#usage)
+  * [Multi-platform build example](#multi-platform-build-example)
 * [Customizing](#customizing)
   * [inputs](#inputs)
   * [outputs](#outputs)
@@ -48,6 +49,43 @@ jobs:
 >       uses: docker/setup-buildx-action@v4
 > ```
 
+### Multi-platform build example
+
+The following example shows how to use this action to build and push a multi-platform image for `linux/amd64` and `linux/arm64` using [Buildx](https://github.com/docker/buildx):
+
+```yaml
+name: ci
+
+on:
+  push:
+    branches:
+      - 'main'
+
+jobs:
+  docker:
+    runs-on: ubuntu-latest
+    steps:
+      -
+        name: Set up QEMU
+        uses: docker/setup-qemu-action@v4
+      -
+        name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v4
+      -
+        name: Login to Docker Hub
+        uses: docker/login-action@v3
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+      -
+        name: Build and push
+        uses: docker/build-push-action@v6
+        with:
+          push: true
+          tags: user/app:latest
+          platforms: linux/amd64,linux/arm64
+```
+
 ## Customizing
 
 ### inputs