Add a release note regarding recent files change.

Refs mantidproject#12425

docs/source/release/v3.14.0/ui.rst

@@ -17,6 +17,7 @@ Project Recovery
 Changes
 #######
 - Project Recovery will no longer save groups, this fixes an issue where it would cause crashes if you deleted a workspace from a group.
+- MantidPlot no longer checks for the existence of files in the "Recent Files" menu. Fixes case where files on slow mounted network drives can cause a lag on MantidPlot startup.
 
 Bugfixes
 ########
@@ -30,4 +31,4 @@ BugFixes
 
 - Fixed issue where an open set of data from ITableWorkspace wouldn't update if the data was changed via python
 
-:ref:`Release 3.14.0 <v3.14.0>`
+:ref:`Release 3.14.0 <v3.14.0>`