Update runtime files

runtime/doc/syntax.txt

@@ -1,4 +1,4 @@
-*syntax.txt*	For Vim version 8.2.  Last change: 2022 Apr 06
+*syntax.txt*	For Vim version 8.2.  Last change: 2022 Apr 24
 
 
 		  VIM REFERENCE MANUAL	  by Bram Moolenaar
@@ -2197,6 +2197,15 @@ $VIMRUNTIME/syntax/syntax.vim).
   mv_finance	 mv_logic	mv_powseries
 
 
+MARKDOWN						*ft-markdown-syntax*
+
+If you have long regions there might be wrong highlighting.  At the cost of
+slowing down displaying, you can have the engine look further back to sync on
+the start of a region, for example 500 lines: >
+
+	:let g:markdown_minlines = 500
+
+
 MATHEMATICA		*mma.vim* *ft-mma-syntax* *ft-mathematica-syntax*
 
 Empty *.m files will automatically be presumed to be Matlab files unless you