[LyX/master] Document parskip change in RELEASE NOTES (#10968)

[Juergen Spitzmueller]

commit 9febb601905b4329615f9f37a6b801cd0e9abaf4
Author: Juergen Spitzmueller <spitz at lyx.org>
Date:   Fri Oct 29 18:01:02 2021 +0200

    Document parskip change in RELEASE NOTES (#10968)
---
 lib/RELEASE-NOTES |    9 +++++++++
 1 files changed, 9 insertions(+), 0 deletions(-)

diff --git a/lib/RELEASE-NOTES b/lib/RELEASE-NOTES
index b779b62..b7e870c 100644
--- a/lib/RELEASE-NOTES
+++ b/lib/RELEASE-NOTES
@@ -220,6 +220,15 @@
 
 !!Caveats when upgrading from earlier versions to 2.4.x
 
+* LyX now uses the parskip package for vertical paragraph separation. Since the
+  output differs from the previous (sub-optimal) approach which applied paragraph
+  separation to sections, lists etc. as well, existing documents
+  are converted to use preamble code that maintains the previous layout.
+  The downside is that the workarea looks as if paragraph indendation rather
+  than paragraph separation was used (output is correct). We encourage you
+  to try if the new layout suits you, remove the respective preamble code
+  and re-set the paragraph separation to use the new layout.
+
 * Autotools monolithic build option for building LyX binaries was removed,
   for compilation speedup use parallel building on multiple cores instead.