runtime(doc): update documentation on tabstop settings

Unify the treatment of tabstop, correct errors and deprecate smarttab
usage.

closes: #17444

Signed-off-by: Damien Lejay <damien@lejay.be>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/doc/quickref.txt b/runtime/doc/quickref.txt
index de902ee..6af2568 100644
--- a/runtime/doc/quickref.txt
+++ b/runtime/doc/quickref.txt
@@ -1,4 +1,4 @@
-*quickref.txt*  For Vim version 9.1.  Last change: 2025 Jun 04
+*quickref.txt*  For Vim version 9.1.  Last change: 2025 Jun 10
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -942,7 +942,7 @@
 'tabclose'	  'tcl'     which tab page to focus when closing a tab
 'tabline'	  'tal'     custom format for the console tab pages line
 'tabpagemax'	  'tpm'     maximum number of tab pages for |-p| and "tab all"
-'tabstop'	  'ts'	    number of spaces that <Tab> in file uses
+'tabstop'	  'ts'	    number of columns between two tab stops
 'tagbsearch'	  'tbs'     use binary searching in tags files
 'tagcase'	  'tc'      how to handle case when searching in tags files
 'tagfunc'	  'tfu'	    function to get list of tag matches