Revised README.md

[tomwheeler]

What was changed

I revised the README to provide a little more depth, include a link to the pnpm command, and made it clear that the other repo will be the main source of documentation about the OMS.

Why?

1. The pnpm commands by themselves aren't enough to successfully run the application, so I included a link to the QuickStart instructions in the other repo since they explain the prerequisite steps.
2. I suspect that some users may not have the pnpm command installed and may not know where to download it, so I included a link to that site.
3. I clarified that the other repo will provide detailed documentation on the project and that what's here is minimal and applies specifically to the web app.
4. I added a mention of the CI/CD for this project since it seemed relevant to the "Building" heading.