clone.2: Reword discussion of CLONE_NEWNS, removing text also in namespaces(7)

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

man2/clone.2

@@ -352,37 +352,20 @@ For further information on network namespaces, see
 Use of this flag requires
 that the process be privileged
 .RB ( CAP_SYS_ADMIN ).
+
 .TP
 .BR CLONE_NEWNS " (since Linux 2.4.19)"
-Start the child in a new mount namespace.
-
-Every process lives in a mount namespace.
-The
-.I namespace
-of a process is the data (the set of mounts) describing the file hierarchy
-as seen by that process.
-After a
-.BR fork (2)
-or
-.BR clone ()
-where the
+If
 .B CLONE_NEWNS
-flag is not set, the child lives in the same mount
-namespace as the parent.
-The system calls
-.BR mount (2)
-and
-.BR umount (2)
-change the mount namespace of the calling process, and hence affect
-all processes that live in the same namespace, but do not affect
-processes in a different mount namespace.
-
-After a
-.BR clone ()
-where the
-.B CLONE_NEWNS
-flag is set, the cloned child is started in a new mount namespace,
+is set, the cloned child is started in a new mount namespace,
 initialized with a copy of the namespace of the parent.
+If
+.B CLONE_NEWNS
+is not set, the child lives in the same mount
+namespace as the parent.
+
+For further information on mount namespaces, see
+.BR namespaces (7).
 
 Only a privileged process (one having the \fBCAP_SYS_ADMIN\fP capability)
 may specify the
@@ -395,6 +378,7 @@ and
 in the same
 .BR clone ()
 call.
+
 .TP
 .BR CLONE_NEWUSER
 (This flag first became meaningful for