add readme

readme.md

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+ecs-deploy-action
+===
+
+What do you mean you don't know what I am? I'm a github action that deploys to your ECS.
+
+Hmm, let me try and clear this up. If you chuck some yaml in your workflow that looks like this:
+
+```yaml
+      - uses: flipgroup/ecs-deploy-action@v1
+        with:
+          cluster: default
+          service: YourServiceName
+          image-overrides: YourContainerName=111111111111.dkr.ecr.ap-southeast-2.amazonaws.com/Repo/YourImageName:${{ env.GITHUB_RUN_NUMBER }}
+```
+Then I will go and update your service the running containers with a new docker image for you. That easy.
+
+What about environment't variables you ask? I'll just copy it over for you and assume you manage that some other way.
+
+I also play nice with [aws-actions/configure-aws-credentials](https://github.com/aws-actions/configure-aws-credentials)