uts_namespaces.7: Add a little more detail on scope of UTS namespaces

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

man7/uts_namespaces.7

@@ -38,6 +38,9 @@ and can be retrieved using
 .BR gethostname (2),
 and
 .BR getdomainname (2).
+Changes made to these identifiers are visible to all other
+processes in the same UTS namespace,
+but are not visible to processes in other UTS namespaces.
 .PP
 .PP
 When a process creates a new UTS namespace using