document our WebID installation process, for dummies

[bennomadic]

• Could include a layman's WebID explanation + screencasts, etc.
• Should be upgraded as the UI evolves.
• With screenshots on main browsers.

@dominique: what do you think about the right timing to do this? I think we should wait until we have a more stable/integrated UI.

I thought it could be good to have a separate package for this (with optional switches from -provider, so it gets included in the templaetes if present and enabled). It could improve maintanability.