The only downside of this new technique is that it is no
longer possible to set XDG_DATA_DIRS to an empty var in kitty.conf
Since an empty XDG_DATA_DIRS breaks lots fo things, I dont think that
is a big concern.
Less intrusive (in some ways) than adding symlinks to ~/.config/fish
Exploits the fact that fish loads scripts from XDG_DATA_DIRS on startup.
Thanks to @page-down for noticing