security/namespace.conf: Update comments

The default Debian comment was not accurate in our config.

security/namespace.conf

@@ -2,12 +2,9 @@
 #
 # See /usr/share/doc/pam-*/txts/README.pam_namespace for more information.
 #
-# Uncommenting the following three lines will polyinstantiate
-# /tmp, /var/tmp and user's home directories. /tmp and /var/tmp will
-# be polyinstantiated based on the MLS level part of the security context as well as user
-# name, Polyinstantion will not be performed for user root and adm for directories
-# /tmp and /var/tmp, whereas home directories will be polyinstantiated for all users.
-# The user name and context is appended to the instance prefix.
+# /tmp, /var/tmp and /run/lock are polyinstantiated on a per-user basis,
+# resulting in each user having a different, private directory mounted
+# at those locations.
 #
 # Note that instance directories do not have to reside inside the
 # polyinstantiated directory. In the examples below, instances of /tmp