Fix reference to docker-compose in README

[jsf9k]

🗣 Description

This pull request updates README.md to use the docker compose syntax instead of the docker-compose syntax.

💭 Motivation and context

The docker compose syntax is the preferred (and only correct) syntax after the changes in cisagov/ansible-role-docker#60.

🧪 Testing

Automated testing passes.

✅ Pre-approval checklist

• This PR has an informative and human-readable title.
• Changes are limited to a single goal - eschew scope creep!
• All relevant type-of-change labels have been added.
• I have read the CONTRIBUTING document.
• These code changes follow cisagov code standards.
• All relevant repo and/or project documentation has been updated to reflect the changes in this PR.
• All new and existing tests pass.

[jsf9k]

Note that the linting checks will pass once cisagov/skeleton-docker#79 is merged and flows down to this repo.

[dav3r]

Stunning!

[jsf9k]

Note that the linting checks will pass once cisagov/skeleton-docker#79 is merged and flows down to this repo.

cisagov/skeleton-docker#79 has been merged and has flowed down to this repo via #49. As predicted, the linting checks now pass.