Make a note that cwd reporting is builtin to fish

shell-integration/fish/vendor_conf.d/kitty-shell-integration.fish

@@ -97,6 +97,8 @@ function __ksi_schedule --on-event fish_prompt -d "Setup kitty integration after
 
     # Enable CWD reporting
     if not contains "no-cwd" $_ksi
+        # This is actually builtin to fish but stupidly gated on TERM
+        # https://github.com/fish-shell/fish-shell/blob/master/share/functions/__fish_config_interactive.fish#L257
         function __ksi_report_cwd --on-variable PWD --description "Report PWD changes to the terminal"
             echo -en "\e]7;kitty-shell-cwd://$hostname$PWD\a"
         end