Create letterhome.py

As you can see, this is a very simple program. That's the point.

I knew almost no programming when I made this. I wanted to write
letters to my parents when I first lived away from home for school
so that my mom would stop nagging me about it when she called.

This was the beginning -- and then it evolved into something more
sophisticated (randomly ordering sentences and paragraphs, drawing
from a larger library of phrases, using better data storage
techniques, etc) -- as I learned more about computing, but... this
was how I started.