Improve readme and fix dep

Readme: (in example) prefix function with _
Dep: add a depency to base_setup in order to use xml id "base.menu_config"

keychain/README.rst

@@ -99,7 +99,7 @@ Usage (for module dev)
 
     import random
 
-    def get_auth(self):
+    def _get_auth(self):
         keychain = self.env['keychain.account']
         if self.env.user.has_group('stock.group_stock_user'):
             retrieve = keychain.suspend_security().retrieve

keychain/__openerp__.py

@@ -17,6 +17,7 @@
     },
     "depends": [
         "base",
+        "base_setup",
     ],
     "data": [
         "security/ir.model.access.csv",