You select the package you want to import and you’re done. But the problem is, you can select only one single object? What if you want to import 20 packages to your project? Kind of annoying to repeat the same process 20 times, isn’t it?
Luckily there’s an easier way. Instead of going for the obvious Add Existing Package, right-click on the project itself. In the context-menu, choose Add, ignore Existing Package and click on Existing Item.
If you have a large number of packages to import, this will save you a few minutes of tedium (or hand-editing a project file).