Update social preview for repository

[anki-code]

Based on kitty's website logo I've made the social preview for xontrib-kitty that's awesome:

@scopatz please open https://github.com/scopatz/xontrib-kitty/settings and set Social preview:

After this the xontrib will have a preview on https://github.com/topics/xontrib

[anki-code]

Please also add kitty and kitty-terminal topics to the repository.