Link virtualenv to repo directory

This reverts a change whereby the installation script would link
the newly-created virtualenv to the `$HOME/.virtualenvs` directory,
which isn't what we want. We *actually* want the virtualenv to link
to the project/repo directory so that `workon <virtualenv>` takes
us to the code that we want to work on.

@Slater-Victoroff, could you take a look please?