GLs example

[lamelizard]

As PR #3 stated (#3's note was about GIs), we do not have an example for GLs yet,
is there a good simple example?

We could do the "Eight queens puzzle" with rocks and kings
-> allow GWFC to insert some rocks and kings and no piece may be able to hit another piece
-> requires 3 GLs (2 for rocks, 1 for kings)
but this is boring (but music or art is probably too much code as a simple example?)