The easy way
Polly recently added a PPA - to add it, run the following:
Then, just select "Polly" to run from the Unity Dash, or run
Outdated instructions that are being kept for future reference:
Fairly simple to run it. This won't install it properly, it'll just download the python files to your home directory and run them. But it works.
If you want to make a launcher, just have it run
You'll want to keep it updated on a regular basis. To do that, run: