man: Improve upgrade-minimal command docs (RHEL-6417)

Making the man pages for the `upgrade-minimal` command clearer about how packages with advisories are upgraded.

Resolves: https://issues.redhat.com/browse/RHEL-6417

doc/command_ref.rst

@@ -1760,12 +1760,14 @@ Upgrade-Minimal Command
 
 ``dnf [options] upgrade-minimal``
     Updates each package to the latest available version that provides a bugfix, enhancement
-    or a fix for a security issue (security).
+    or a fix for a security issue (security). Newer updates not mentioned in any advisories
+    are ignored.
 
 ``dnf [options] upgrade-minimal <package-spec>...``
     Updates each specified package to the latest available version that provides
-    a bugfix, enhancement or a fix for security issue (security). Updates
-    dependencies as necessary.
+    a bugfix, enhancement or a fix for security issue (security). Newer updates
+    not mentioned in any advisories are ignored. Dependencies are updated
+    as needed.
 
 .. _specifying_packages-label: