Explain sort order options in fish completions

misc/auto-completion/fish/nnn.fish

@@ -38,7 +38,7 @@ complete -c nnn -s R    -d 'disable rollover at edges'
 complete -c nnn -s s -r -d 'load session by name' -x -a '@\t"last session" (ls $sessions_dir)'
 complete -c nnn -s S    -d 'persistent session'
 complete -c nnn -s t -r -d 'timeout in seconds to lock'
-complete -c nnn -s T -r -d 'a d e r s t v'
+complete -c nnn -s T -r -d 'sort order' -x -a "a\t'apparent disk usage' d\t'disk usage' e\t'extension' r\t'reverse' s\t'size' t\t'time' v\t'version'"
 complete -c nnn -s u    -d 'use selection (no prompt)'
 complete -c nnn -s U    -d 'show user and group'
 complete -c nnn -s V    -d 'show program version and exit'