Update the doc to reflect how we specify bricks in projects

[tengstrand]

Update the doc to reflect that we now use :local/root when specifying which bricks to include in a project.

For example this sentence:
If you look at the directory projects/realworld-backend, you will see a standard deps.edn file. The magic here is the project's deps.edn file which refers to the sources, resources and tests of actual components and bases.

Here we could also link to the deps.edn file.