Feature/issue 456 add temperature to motd also new pytemp.py command

I created the pytemp.py for my RetroPie here that I've been playing with and had already added it to my .bashrc... then I was poking around this repo and saw Issue 456 (https://github.com/petrockblog/RetroPie-Setup/issues/456),  and decided perhaps I should contribute.  

It spits out the current CPU and GPU temperatures in both degrees C and degrees F.  

I have no idea if I'm putting these changes and the pytemp.py file into the correct location in the repo, but here is what I have so far.  Thoughts?