Update README.md

[hoerstl]

In a recent PR (Improving the Devcontainer) which was merged, we made significant improvements to the development experience. a.k.a ...

We added a devcontainer to the repository! We should modify out README.md file to reflect these changes in setup and development.

[bledsoef]

@hoerstl it would probably be a good idea for you and Josh to take care of this as you are the ones who made the devcontainer changes.