Add the output of the example code

[kinow]

Hi,

I am trying pluggy, and after reading the README.md short example I thought I knew what would be the output, but had to run the code to confirm.

This PR adds Python comments to the code block with the results. But perhaps it could go somewhere else if others have any suggestions?

Thanks for pluggy
Bruno

[kinow]

Ah, just realized the readthedocs page has the results. Feel free to close if you prefer to have just the code in the README.md 👍

[goodboy]

@kinow I'm cool with this - helps with groking the example at a glance.

I wonder can we present it in the readme in a little more of a "shell output"-y way like with literal blocks?

[kinow]

@goodboy good idea. Copied the text from the readthedocs site and updated the commit 👍