Add Example Custom Filter to Wiki

[TheNferno]

I had asked for help on the MCA Magic Discord with the custom filters and @arvitus graciously helped me out and provided code for the filter to select chunks that had generated structures. I feel that this would be a useful filter for other so I thought it would be helpful to add it to the examples section in the wiki. The filter is region.get("structures").get("References").size() > 0

[arvitus]

It's also important to note that the filter will probably only work on certain mc versions as the chunk structure of mc changes regularly