Add tutorial: setting-up Bluetooth - PulseAudio

Probably needs more work, but this is a good stage to ask for comments.
On Windows the `tutorials` page did not look OK:
![tutorial_on_win7](https://cloud.githubusercontent.com/assets/8142081/5077594/11e1ed2a-6ea5-11e4-9b5d-810e3c4345cd.png)

But that could well be a jekyll on win artefact.

learned.
I only "knew" about the way to paste pictures in an issue.
This way is much better.
Question 1: there is an image main-menu.png that lacks the bluetooth option.
Have made an extra `main-menu-incl-bluetooth.png`
Or would you want to replace the original?
Question 2: how to synchronize the colors in the images, so they all look alike?
Mine are white, so there is no distinct border.