Run postgres in container

[nathansgithub]

Description

I updated the instructions for running locally and added commands in package.json according to issue #229.

Related Issue

229

Motivation and Context

It reduces the friction for new contributors. Since Docker Compose is already a project dependency, it makes sense to run Postgres there instead of making contributors setup their own database.

How Has This Been Tested?

I removed all existing Docker containers I had running and walked through the updated instructions in CONTRIBUTING.md.

Checklist:

• [x] My code follows the code style of this project.
• [x] My change requires a change to the documentation.
• [x] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.
• [N/A] I have added tests to cover my changes.
• [N/A] All new and existing tests passed.

[nathansgithub]

Ok, they are squashed!

[nathansgithub]

@tcaddy That makes sense. I added a named volume and also removed the specified Postgres version so it will use the latest version.

[nathansgithub]

@tcaddy I went ahead and squashed that into the other commit too. Let me know if that looks good. Thanks for reviewing this!