figure rendering in Readme.md

[MartinHeroux]

At present the pliffy logo and the example plot are not appearing on the rendered README.md on github, and this despite using the exact same format as I used for spike2py.

This might be because of the way I have to refer to the figures using the following call:

[![pliffy](https://raw.githubusercontent.com/MartinHeroux/pliffy/master/docs/source/img/pliffy_650x200.png)]

It might be that this source needs to be updated...not sure. I will check again tomorrow morning to see if my pictures are rendering properly. If not, will have to troubleshoot why this is not working.

[bbelderbos]

https://raw.githubusercontent.com/MartinHeroux/pliffy/master/docs/source/img/pliffy_650x200.png gives me a 404, how did you get to this link?

[MartinHeroux]

Fixed. The button use to say raw file, but now you simply have to click on the download button and rather than downloading the image, it opens up in a new browser window; it is that url that needs to be added to the README.md