volo.baseDir is to specify where dependencies should be installed in
the project when `volo add` is used, not for specifying what to
extract.
You can use a volofile with an 'onAdd' hook in it. The onAdd hook is
called whenever your library is added as a dependency.
Example from the tests:
https://github.com/volojs/volo/tree/master/tests/commands/add/support/addable
So if you place a similar volofile in the root of your repo, it will
get called when `volo add` fetches the code, and you can have it move
up the src directory to the root of your directory, and clean up any
files, including deleting the volofile with the 'onAdd' hook.
James