Add tutorials folder

[mmaelicke]

Add a new top-level folder for tutorial notebooks. Put it at ./tutorials.

The first should be about reading files and pushing them to metacatalog

I would suggest to keep the filenames lowercase with an underscore instead of whitespace and prefixed by a double-digit number like 01_getting_started, 02_tools_overview etc.

[mmaelicke]

I think this will be done differently. I will close this issue now.