chown.2: NOTES: Add some subheadings

(No content changes.)

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man2/chown.2

@@ -328,25 +328,7 @@ used only by the superuser (that is, ordinary users cannot give away files).
 .BR fchownat ():
 POSIX.1-2008.
 .SH NOTES
-The original Linux
-.BR chown (),
-.BR fchown (),
-and
-.BR lchown ()
-system calls supported only 16-bit user and group IDs.
-Subsequently, Linux 2.4 added
-.BR chown32 (),
-.BR fchown32 (),
-and
-.BR lchown32 (),
-supporting 32-bit IDs.
-The glibc
-.BR chown (),
-.BR fchown (),
-and
-.BR lchown ()
-wrapper functions transparently deal with the variations across kernel versions.
-
+.SS Ownership of new files
 When a new file is created (by, for example,
 .BR open (2)
 or
@@ -395,7 +377,7 @@ mount options are supported by ext2, ext3, ext4, and XFS.
 Filesystems that don't support these mount options follow the
 .IR "\-o\ nogrpid"
 rules.
-.PP
+.SS NFS
 The
 .BR chown ()
 semantics are deliberately violated on NFS filesystems
@@ -408,6 +390,25 @@ Client side
 caching may lead to a delay between the time where ownership have
 been changed to allow access for a user and the time where the file can
 actually be accessed by the user on other clients.
+.SS Historical details
+The original Linux
+.BR chown (),
+.BR fchown (),
+and
+.BR lchown ()
+system calls supported only 16-bit user and group IDs.
+Subsequently, Linux 2.4 added
+.BR chown32 (),
+.BR fchown32 (),
+and
+.BR lchown32 (),
+supporting 32-bit IDs.
+The glibc
+.BR chown (),
+.BR fchown (),
+and
+.BR lchown ()
+wrapper functions transparently deal with the variations across kernel versions.
 
 In versions of Linux prior to 2.1.81 (and distinct from 2.1.46),
 .BR chown ()