[ADD] better documentation

[FIX] mapping error

field_rrule/README.rst

@@ -21,6 +21,10 @@ To use this module, you need to:
 
 Technically, this is a wrapper around serialized fields. The value always will be a subclass of dateutil's ``rruleset``. For technical reasons, this class overrides ``__iter__``, so if you need a proper ``rruleset``, call the value: ``my_browse_record.my_field_of_type_rrule()`` - this gives you a vanilla ``rruleset``.
 
+If you want to pass a default, use the internal representation you'll find in the database - a list of dictionaries with the keyword arguments to be passed to rrule's constructor and a `type` field that for now can only be `rrule`: A context of ``{"default_rrule": [{"count": 1, "freq": 1, "type": "rrule", "interval": 1, "bymonthday": [1]}]}`` would give you a default for the field ``rrule`` which occurs one time at the first of the month.
+
+Further, as this is a serialized field, a value of `not set` will be represented in the database as ``'null'`` - this is then also what you have to search for when you need records with your field unset.
+
 Known issues / Roadmap
 ======================
 

field_rrule/static/src/js/field_rrule.js

@@ -75,7 +75,7 @@ openerp.field_rrule = function(instance)
                     '%T': 'hh:mm:ss',
                     '%I': 'h',
                     '%j': '', // day of the year unsuported
-                    '%m': 'm',
+                    '%m': 'mm',
                     '%M': 'mm',
                     '%p': 't',
                     '%S': 'ss',