Request: tutorial for basic functions

Hi there,

I'm trying to build a substrate ('clean_up') but the documentation, in my opinion, is not very clear about what the functions or their arguments are specifically. For instance, 'roles' in clean_up is only shown to be a sequence of strings, not what those strings should be. If this information is located somewhere in the document or in dmlab2d, it is not easy to find. For ease of usage, I think some worked examples of building the substrates in Python and showcase the differences in usage would be very beneficial.

Start by reviewing the documentation for the clean_up substrate and checking dmlab2d for the definitions of its functions and arguments, especially roles. Add worked Python examples that show how to build substrates and clarify the differences in usage, including what values such as the roles strings should contain.

Written by the indexing model from the issue text.