Add to readme directions how to properly import project into IDE.

[ccorder-xpxn]

This is more of a suggestion than issue. But in IntelliJ, when I try to import this project from existing sources. The recommended project structure ends up being a confangled mess of source folders and modules with names like main22, main23, test2 etc.. Ideally we could have each module being the root of the exercise e.g. 3.07-Exercise-DeclareFlavors.

I know I can just unzip the folder and run all gradle commands from the command line, but IDE functionality just makes things more convenient.

[dnbit]

@ccorder-xpxn This repo is a bunch of projects, not a single one. You need to open each folder as a separate project.