runtime(doc): rename variable for pandoc markdown support

fixes: #15141

Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/doc/syntax.txt b/runtime/doc/syntax.txt
index 57db7cb..ee8d689 100644
--- a/runtime/doc/syntax.txt
+++ b/runtime/doc/syntax.txt
@@ -1,4 +1,4 @@
-*syntax.txt*	For Vim version 9.1.  Last change: 2024 Jun 22
+*syntax.txt*	For Vim version 9.1.  Last change: 2024 Jul 03
 
 
 		  VIM REFERENCE MANUAL	  by Bram Moolenaar
@@ -2518,9 +2518,9 @@
 
 By default, markdown files will be detected as filetype "markdown".
 Alternatively, you may want them to be detected as filetype "pandoc" instead.
-To do so, set the following: >
+To do so, set the *g:filetype_md* var: >
 
-	:let g:markdown_md = 'pandoc'
+	:let g:filetype_md = 'pandoc'
 
 The pandoc syntax plugin uses |conceal| for pretty highlighting. Default is 1 >