docs(news): add linematch (#20927)

runtime/doc/news.txt

@@ -41,9 +41,17 @@ The following new APIs or features were added.
 
 • When using Nvim inside tmux 3.2 or later, the default clipboard provider
   will now copy to the system clipboard. |provider-clipboard|
+
 • 'splitkeep' option to control the scroll behavior of horizontal splits.
+
 • |nvim_select_popupmenu_item()| now supports |cmdline-completion| popup menu.
 
+• |'diffopt'| now includes a `linematch` option to enable a second-stage diff
+  on individual hunks to provide much more accurate diffs. This option is also
+  available to |vim.diff()|
+
+  See https://github.com/neovim/neovim/pull/14537.
+
 ==============================================================================
 CHANGED FEATURES                                                 *news-changes*
 

runtime/doc/vim_diff.txt

@@ -267,6 +267,7 @@ Options:
   'tabline'     %@Func@foo%X can call any function on mouse-click
   'winblend'    pseudo-transparency in floating windows |api-floatwin|
   'winhighlight' window-local highlights
+  'diffopt'     has the option `linematch`.
 
 Signs:
   Signs are removed if the associated line is deleted.