update NEWS file a bit

NEWS

 release/004.061 (2016-04-21)
 
     [os] Add some parameters to the base::os::debian class to make apt use
-    a directory other than /tmp for its cache. This is to get around
-    setting /tmp to noexec. Note that the default is to continue using
-    /tmp as apt's cache directory, so upgrading to this version is
-    safe. (adamhl)
+    a directory other than /tmp for its cache.
+
+    Reason: The apt utility when installing or uninstalling a package puts
+    its temporary files, including scripts it needs to execute, in
+    /tmp. If the /tmp partition is set to noexec (as recommended by
+    security advisors), then one cannot run any executable out of the /tmp
+    directory. The result is that the package install will not finish
+    properly. The new parameters in the base::os::debian class tell apt to
+    use /var/cache/apt/tmp as its temporary cache directory getting around
+    the /tmp noexec problem.
+
+    Note that the default is to continue using /tmp as apt's cache
+    directory, so upgrading to this version is safe. (adamhl)
 
 release/004.060 (2016-04-04)