#451: Minor README update

[rbrglez]

Description of the Issue:

I am encountering a NameError when running the script failing.py. The issue appears to be related to the way I am importing the edalize module. When importing the module as described in the README (from edalize import *), I get an error. However, when importing only the get_edatool function (from edalize.edatool import get_edatool), the script runs successfully.

Resolution:

I've updated README