tweak documentation

doc/configuring.rst

@@ -171,6 +171,10 @@ you gain access to *Borg* placeholders. *archive* shows an example of that.
 Interpolation is not performed on any setting whose name is given in 
 :ref:`do_not_expand`.
 
+If desired, you can create your own placeholders.  Simply add a named value to 
+an appropriate configuration file.  *Assimilate* will not recognize it and so 
+will ignore it, but the value is available to be used as a placeholder.
+
 
 .. _paths:
 

doc/monitoring.rst

@@ -77,10 +77,13 @@ Overdue
 -------
 
 *Assimilate* provides the *overdue* command that can be used to determine which 
-of your repositories are overdue for backup.  It can report on many configs, not 
-just the active config.  This is useful if you are supporting many repositories 
-as it can use ssh to query remote backups.  It uses the :ref:`overdue setting` 
-setting to specify the desired configs.
+of your repositories are overdue for backup.  Unlike the :ref:`due command 
+<due>`, it is not limited to reporting on the active config and can even report 
+on remote configs via *ssh*.  As such, *overdue* is generally used to present 
+a summary of all of your backups.
+
+It uses the :ref:`overdue setting <overdue setting>` to specify the desired 
+configs, which is a composite setting that consists of:
 
 | *max_age* (how old a repository must be to constitute failure)
 | *sentinel_root* (default directory for sentinel files)