Documentation updates, improvements.

* Updated documentation at `doc/sources/markdown`
* Left the `templates/app/assets/nib/` and `nib` injection untouched -- **i was not able to import `nib` anyhow**. If you can use `nib` without just copying its files to the `app/assets/stylesheets` directory - provide a valid step-by-step manual, please. Until that, it is an improvement. I really insist you to merge this change.