Copyright assignment for treesit-fold

[Mattias]

Hi,

I contributed to treesit-fold and the authors asked us to complete the 
paperwork for copyright assignment: 
https://github.com/emacs-tree-sitter/treesit-fold/issues/11

It looks like I need to write to this mailing list to do it 
electronically so here I am, needing some help :-)

Thanks in advance to anyone willing to give its time to help me do it,

Mattias