[ADD] example

auth_dynamic_groups/README.md

@@ -13,3 +13,18 @@ truthy if the user is supposed to be a member of the group and falsy if not.
 There is a constraint on the field to check for validity if this expression.
 When you're satisfied, click the button `Evaluate` to prefill the group's
 members. The condition will be checked now for every user who logs in.
+
+Example
+-------
+We have a group called `Amsterdam` and want it to contain all users from
+city of Amsterdam. So we use the membership condition
+
+```
+user.partner_id.city == 'Amsterdam'
+```
+
+Now we can be sure every user living in this city is in the right group, and we
+can start assigning local menus to it, adjust permissions, etc. Keep in mind
+that view overrides can also be restricted by a group id, this gives a lot of
+possibilities to dynamically adapt views based on arbitrary properties
+reachable via the user record.