Get Leo's installation path automatically (if installed with pip)

[boltex]

Ville M. Vainio proposed that the Leo path setting could be set automatically if Leo was installed with pip.

So a good improvement would be that on installation, and on upgrade, check with: python -c "import leo; import os; print(os.path.dirname(leo.__file__))"

(or somesuch) to get the Leo Editor's installation path and set it automatically (if not already set), allowing the user to skip this step before its first LeoInteg usage.