Update Homebrew-and-Python to describe install

I believe the Homebrew-and-Python page could use a description on how to exactly install Python 2.X and 3.X with Homebrew. 

The syntax is written to my best knowledge (but likely wrong), please update this so that it is correct. Finding out the correct syntax is what actually motivated me to update this page in the first place. I'm hoping that this will clarify to the community (or at least me) on how to exactly install Python 2.X and 3.X with Homebrew.

Keep up the amazing work!