RELNOTES: mention moving filesystems to section 4

Fixes:		1687d7 (move filesystems to s4)
Reported by:	mhorne
Reviewed by:	imp, mhorne
Pull Request:	freebsd/freebsd-src#1289

RELNOTES

@@ -10,13 +10,16 @@ newline.  Entries should be separated by a newline.
 
 Changes to this file should not be MFCed.
 
-
 822ca3276345:
 	byacc was updated to 20240109.
 
 21817992b331:
 	ncurses was updated to 6.5.
 
+1687d77197c0:
+	Filesystem manual pages have been moved to section four.
+	Please check ports you are maintaining for crossreferences.
+
 8aac90f18aef:
 	new MAC/do policy and mdo(1) utility which enables a user to
 	become another user without the requirement of setuid root.