Readme, default_, fields.depends, fields.Function

please reject everything i am wrong with..

i added some text about default_values, fields.depends (please correct me if i got the news from 3.2 wrong!!), fields.Function
Also i added a readme to have a list of all available documentation.
maybe this should be put to a different place (fields) at some point...
Not sure if you know, but Function won't be recomputed on client side. To achive it (always get the correct value on the client side), you can combine Function fields with on_change_with, something like:
```
is_owned_by_me = fields.Function(fields.Boolean('XXX'), 'on_change_with_is_owned_by_me')

@fields.depends('owner')
def on_change_with_is_owned_by_me(self, name=None):
     return self.owner == 'me'
```
So if the field is displayed on a view, it will be updated every time the owner field is changed. 

I think its worth to mention this case also.