Use `label` over `name` for build step config in examples
Use `label` over `name` for build step config in examples

I noticed that `name` was being used instead of `label` in the example pipeline snippets in the README.md file, so I thought I'd create a small PR to make them consistent with the command build step documentation.
buildkite-plugins/docker-compose-buildkite-plugin,buildkite/docker-compose-buildkite-plugin,buildkite-plugins/docker-compose